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 $91.91   5.512%   $96.9761   $96.98   $97.00   $97.00  
  Purchase #2 $112.94   11.200%   $125.5893   $125.59   $125.60   $125.60  
  Purchase #3 $23.90   4.844%   $25.0577   $25.06   $25.05   $25.10  
  Purchase #4 $227.35   12.357%   $255.4436   $255.44   $255.45   $255.40  
  Purchase #5 $110.43   12.317%   $124.0317   $124.03   $124.05   $124.00  
  Purchase #6 $172.31   13.435%   $195.4598   $195.46   $195.45   $195.50  
  Purchase #7 $91.32   12.581%   $102.809   $102.81   $102.80   $102.80  
  7 purchase totals = $830.16       $925.3672   $925.37   $925.40   $925.40