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 $93.83   8.673%   $101.9679   $101.97   $101.95   $102.00  
  Purchase #2 $51.58   5.267%   $54.2967   $54.30   $54.30   $54.30  
  Purchase #3 $134.98   7.360%   $144.9145   $144.91   $144.90   $144.90  
  Purchase #4 $195.90   6.285%   $208.2123   $208.21   $208.20   $208.20  
  Purchase #5 $50.37   8.779%   $54.792   $54.79   $54.80   $54.80  
  Purchase #6 $135.94   10.585%   $150.3292   $150.33   $150.35   $150.30  
  Purchase #7 $222.85   9.450%   $243.9093   $243.91   $243.90   $243.90  
  7 purchase totals = $885.45       $958.4219   $958.42   $958.40   $958.40