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 $62.84   5.696%   $66.4194   $66.42   $66.40   $66.40  
  Purchase #2 $248.71   11.670%   $277.7345   $277.73   $277.75   $277.70  
  Purchase #3 $73.52   8.145%   $79.5082   $79.51   $79.50   $79.50  
  Purchase #4 $194.26   12.276%   $218.1074   $218.11   $218.10   $218.10  
  Purchase #5 $9.87   12.589%   $11.1125   $11.11   $11.10   $11.10  
  Purchase #6 $201.32   12.703%   $226.8937   $226.89   $226.90   $226.90  
  Purchase #7 $70.92   5.396%   $74.7468   $74.75   $74.75   $74.70  
  7 purchase totals = $861.44       $954.5225   $954.52   $954.50   $954.40