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 $143.56   7.618%   $154.4964   $154.50   $154.50   $154.50  
  Purchase #2 $229.91   7.152%   $246.3532   $246.35   $246.35   $246.40  
  Purchase #3 $213.27   12.729%   $240.4171   $240.42   $240.40   $240.40  
  Purchase #4 $57.76   6.587%   $61.5647   $61.56   $61.55   $61.60  
  Purchase #5 $51.74   11.530%   $57.7056   $57.71   $57.70   $57.70  
  Purchase #6 $121.62   9.252%   $132.8723   $132.87   $132.85   $132.90  
  Purchase #7 $240.28   8.544%   $260.8095   $260.81   $260.80   $260.80  
  7 purchase totals = $1,058.14       $1,154.2188   $1,154.22   $1,154.15   $1,154.30