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 $48.94   8.696%   $53.1958   $53.20   $53.20   $53.20  
  Purchase #2 $148.69   5.353%   $156.6494   $156.65   $156.65   $156.60  
  Purchase #3 $94.70   13.351%   $107.3434   $107.34   $107.35   $107.30  
  Purchase #4 $152.46   7.570%   $164.0012   $164.00   $164.00   $164.00  
  Purchase #5 $36.88   5.616%   $38.9512   $38.95   $38.95   $39.00  
  Purchase #6 $243.89   7.121%   $261.2574   $261.26   $261.25   $261.30  
  Purchase #7 $238.54   10.504%   $263.5962   $263.60   $263.60   $263.60  
  7 purchase totals = $964.10       $1,044.9946   $1,045.00   $1,045.00   $1,045.00