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 $149.56   11.241%   $166.372   $166.37   $166.35   $166.40  
  Purchase #2 $238.88   12.187%   $267.9923   $267.99   $268.00   $268.00  
  Purchase #3 $187.38   7.631%   $201.679   $201.68   $201.70   $201.70  
  Purchase #4 $46.45   12.132%   $52.0853   $52.09   $52.10   $52.10  
  Purchase #5 $76.38   7.286%   $81.945   $81.95   $81.95   $81.90  
  Purchase #6 $194.85   10.348%   $215.0131   $215.01   $215.00   $215.00  
  Purchase #7 $36.79   7.738%   $39.6368   $39.64   $39.65   $39.60  
  7 purchase totals = $930.29       $1,024.7235   $1,024.73   $1,024.75   $1,024.70