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 $155.48   8.422%   $168.5745   $168.57   $168.55   $168.60  
  Purchase #2 $243.25   4.401%   $253.9554   $253.96   $253.95   $254.00  
  Purchase #3 $134.93   7.416%   $144.9364   $144.94   $144.95   $144.90  
  Purchase #4 $92.84   12.380%   $104.3336   $104.33   $104.35   $104.30  
  Purchase #5 $237.55   7.265%   $254.808   $254.81   $254.80   $254.80  
  Purchase #6 $212.80   3.664%   $220.597   $220.60   $220.60   $220.60  
  Purchase #7 $51.78   13.563%   $58.8029   $58.80   $58.80   $58.80  
  7 purchase totals = $1,128.63       $1,206.0078   $1,206.01   $1,206.00   $1,206.00