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 $76.52   12.183%   $85.8424   $85.84   $85.85   $85.80  
  Purchase #2 $95.81   7.126%   $102.6374   $102.64   $102.65   $102.60  
  Purchase #3 $180.63   3.796%   $187.4867   $187.49   $187.50   $187.50  
  Purchase #4 $210.29   6.791%   $224.5708   $224.57   $224.55   $224.60  
  Purchase #5 $137.32   6.799%   $146.6564   $146.66   $146.65   $146.70  
  Purchase #6 $191.33   12.697%   $215.6232   $215.62   $215.60   $215.60  
  Purchase #7 $202.94   11.359%   $225.992   $225.99   $226.00   $226.00  
  7 purchase totals = $1,094.84       $1,188.8089   $1,188.81   $1,188.80   $1,188.80