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 $187.83   3.548%   $194.4942   $194.49   $194.50   $194.50  
  Purchase #2 $58.81   7.745%   $63.3648   $63.36   $63.35   $63.40  
  Purchase #3 $109.45   9.438%   $119.7799   $119.78   $119.80   $119.80  
  Purchase #4 $149.29   12.109%   $167.3675   $167.37   $167.35   $167.40  
  Purchase #5 $88.43   9.115%   $96.4904   $96.49   $96.50   $96.50  
  Purchase #6 $84.50   3.604%   $87.5454   $87.55   $87.55   $87.50  
  Purchase #7 $182.46   11.589%   $203.6053   $203.61   $203.60   $203.60  
  7 purchase totals = $860.77       $932.6475   $932.65   $932.65   $932.70