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 $203.78   5.489%   $214.9655   $214.97   $214.95   $215.00  
  Purchase #2 $181.89   11.551%   $202.9001   $202.90   $202.90   $202.90  
  Purchase #3 $51.78   12.573%   $58.2903   $58.29   $58.30   $58.30  
  Purchase #4 $95.91   5.713%   $101.3893   $101.39   $101.40   $101.40  
  Purchase #5 $63.41   10.234%   $69.8994   $69.90   $69.90   $69.90  
  Purchase #6 $177.80   5.483%   $187.5488   $187.55   $187.55   $187.50  
  Purchase #7 $98.97   7.596%   $106.4878   $106.49   $106.50   $106.50  
  7 purchase totals = $873.54       $941.4812   $941.49   $941.50   $941.50