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 $91.76   12.662%   $103.3787   $103.38   $103.40   $103.40  
  Purchase #2 $76.84   11.590%   $85.7458   $85.75   $85.75   $85.70  
  Purchase #3 $20.44   12.312%   $22.9566   $22.96   $22.95   $23.00  
  Purchase #4 $225.94   7.386%   $242.6279   $242.63   $242.65   $242.60  
  Purchase #5 $211.51   7.581%   $227.5446   $227.54   $227.55   $227.50  
  Purchase #6 $217.58   3.225%   $224.597   $224.60   $224.60   $224.60  
  Purchase #7 $218.77   7.190%   $234.4996   $234.50   $234.50   $234.50  
  7 purchase totals = $1,062.84       $1,141.3502   $1,141.36   $1,141.40   $1,141.30