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 $54.52   12.477%   $61.3225   $61.32   $61.30   $61.30  
  Purchase #2 $218.74   13.131%   $247.4627   $247.46   $247.45   $247.50  
  Purchase #3 $161.52   10.174%   $177.953   $177.95   $177.95   $178.00  
  Purchase #4 $91.88   10.431%   $101.464   $101.46   $101.45   $101.50  
  Purchase #5 $180.99   12.372%   $203.3821   $203.38   $203.40   $203.40  
  Purchase #6 $60.56   9.496%   $66.3108   $66.31   $66.30   $66.30  
  Purchase #7 $31.55   10.807%   $34.9596   $34.96   $34.95   $35.00  
  7 purchase totals = $799.76       $892.8547   $892.84   $892.80   $893.00