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 $234.91   10.116%   $258.6735   $258.67   $258.65   $258.70  
  Purchase #2 $26.60   4.835%   $27.8861   $27.89   $27.90   $27.90  
  Purchase #3 $213.29   11.136%   $237.042   $237.04   $237.05   $237.00  
  Purchase #4 $76.50   7.665%   $82.3637   $82.36   $82.35   $82.40  
  Purchase #5 $45.38   3.276%   $46.8666   $46.87   $46.85   $46.90  
  Purchase #6 $57.98   13.759%   $65.9575   $65.96   $65.95   $66.00  
  Purchase #7 $203.45   7.690%   $219.0953   $219.10   $219.10   $219.10  
  7 purchase totals = $858.11       $937.8847   $937.89   $937.85   $938.00