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 $179.58   8.827%   $195.4315   $195.43   $195.45   $195.40  
  Purchase #2 $229.40   7.286%   $246.1141   $246.11   $246.10   $246.10  
  Purchase #3 $236.41   8.837%   $257.3016   $257.30   $257.30   $257.30  
  Purchase #4 $31.81   12.654%   $35.8352   $35.84   $35.85   $35.80  
  Purchase #5 $169.41   6.605%   $180.5995   $180.60   $180.60   $180.60  
  Purchase #6 $235.68   10.462%   $260.3368   $260.34   $260.35   $260.30  
  Purchase #7 $73.41   8.284%   $79.4913   $79.49   $79.50   $79.50  
  7 purchase totals = $1,155.70       $1,255.1100   $1,255.11   $1,255.15   $1,255.00