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 $52.98   11.454%   $59.0483   $59.05   $59.05   $59.00  
  Purchase #2 $229.46   8.692%   $249.4047   $249.40   $249.40   $249.40  
  Purchase #3 $122.92   10.188%   $135.4431   $135.44   $135.45   $135.40  
  Purchase #4 $198.89   3.132%   $205.1192   $205.12   $205.10   $205.10  
  Purchase #5 $63.89   5.495%   $67.4008   $67.40   $67.40   $67.40  
  Purchase #6 $153.57   8.521%   $166.6557   $166.66   $166.65   $166.70  
  Purchase #7 $43.52   3.146%   $44.8891   $44.89   $44.90   $44.90  
  7 purchase totals = $865.23       $927.9609   $927.96   $927.95   $927.90