Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $239.60   11.620%   $267.4415   $267.44   $267.45   $267.40  
  Purchase #2 $163.36   13.632%   $185.6292   $185.63   $185.65   $185.60  
  Purchase #3 $210.39   13.397%   $238.5759   $238.58   $238.60   $238.60  
  Purchase #4 $149.69   6.772%   $159.827   $159.83   $159.85   $159.80  
  Purchase #5 $120.94   9.796%   $132.7873   $132.79   $132.80   $132.80  
  Purchase #6 $240.33   12.267%   $269.8113   $269.81   $269.80   $269.80  
  Purchase #7 $102.93   7.498%   $110.6477   $110.65   $110.65   $110.60  
  7 purchase totals = $1,227.24       $1,364.7199   $1,364.73   $1,364.80   $1,364.60