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 $43.78   7.140%   $46.9059   $46.91   $46.90   $46.90  
  Purchase #2 $233.68   12.174%   $262.1282   $262.13   $262.15   $262.10  
  Purchase #3 $61.80   10.872%   $68.5189   $68.52   $68.50   $68.50  
  Purchase #4 $115.69   7.265%   $124.0949   $124.09   $124.10   $124.10  
  Purchase #5 $101.90   5.204%   $107.2029   $107.20   $107.20   $107.20  
  Purchase #6 $36.68   13.234%   $41.5342   $41.53   $41.55   $41.50  
  Purchase #7 $172.43   6.848%   $184.238   $184.24   $184.25   $184.20  
  7 purchase totals = $765.96       $834.6230   $834.62   $834.65   $834.50