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 $176.90   10.756%   $195.9274   $195.93   $195.95   $195.90  
  Purchase #2 $213.29   11.838%   $238.5393   $238.54   $238.55   $238.50  
  Purchase #3 $201.79   4.168%   $210.2006   $210.20   $210.20   $210.20  
  Purchase #4 $48.28   5.723%   $51.0431   $51.04   $51.05   $51.00  
  Purchase #5 $151.78   12.381%   $170.5719   $170.57   $170.55   $170.60  
  Purchase #6 $140.98   12.855%   $159.103   $159.10   $159.10   $159.10  
  Purchase #7 $99.85   13.329%   $113.159   $113.16   $113.15   $113.20  
  7 purchase totals = $1,032.87       $1,138.5443   $1,138.54   $1,138.55   $1,138.50