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 $77.96   13.566%   $88.5361   $88.54   $88.55   $88.50  
  Purchase #2 $239.81   8.573%   $260.3689   $260.37   $260.35   $260.40  
  Purchase #3 $156.67   4.165%   $163.1953   $163.20   $163.20   $163.20  
  Purchase #4 $111.73   9.795%   $122.674   $122.67   $122.65   $122.70  
  Purchase #5 $18.59   13.776%   $21.151   $21.15   $21.15   $21.20  
  Purchase #6 $246.64   8.808%   $268.3641   $268.36   $268.35   $268.40  
  Purchase #7 $113.75   9.449%   $124.4982   $124.50   $124.50   $124.50  
  7 purchase totals = $965.15       $1,048.7876   $1,048.79   $1,048.75   $1,048.90