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 $45.57   12.337%   $51.192   $51.19   $51.20   $51.20  
  Purchase #2 $84.61   4.308%   $88.255   $88.26   $88.25   $88.30  
  Purchase #3 $124.50   7.261%   $133.5399   $133.54   $133.55   $133.50  
  Purchase #4 $164.94   9.338%   $180.3421   $180.34   $180.35   $180.30  
  Purchase #5 $246.90   6.711%   $263.4695   $263.47   $263.45   $263.50  
  Purchase #6 $242.66   13.343%   $275.0381   $275.04   $275.05   $275.00  
  Purchase #7 $36.86   7.822%   $39.7432   $39.74   $39.75   $39.70  
  7 purchase totals = $946.04       $1,031.5798   $1,031.58   $1,031.60   $1,031.50