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 $105.33   12.720%   $118.728   $118.73   $118.75   $118.70  
  Purchase #2 $97.49   11.186%   $108.3952   $108.40   $108.40   $108.40  
  Purchase #3 $149.92   13.366%   $169.9583   $169.96   $169.95   $170.00  
  Purchase #4 $189.34   13.311%   $214.543   $214.54   $214.55   $214.50  
  Purchase #5 $182.29   10.728%   $201.8461   $201.85   $201.85   $201.80  
  Purchase #6 $179.99   3.316%   $185.9585   $185.96   $185.95   $186.00  
  Purchase #7 $16.90   8.213%   $18.288   $18.29   $18.30   $18.30  
  7 purchase totals = $921.26       $1,017.7171   $1,017.73   $1,017.75   $1,017.70