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 $201.59   6.162%   $214.012   $214.01   $214.00   $214.00  
  Purchase #2 $28.49   13.391%   $32.3051   $32.31   $32.30   $32.30  
  Purchase #3 $116.62   12.435%   $131.1217   $131.12   $131.10   $131.10  
  Purchase #4 $44.34   6.265%   $47.1179   $47.12   $47.10   $47.10  
  Purchase #5 $196.87   12.311%   $221.1067   $221.11   $221.10   $221.10  
  Purchase #6 $214.74   11.457%   $239.3428   $239.34   $239.35   $239.30  
  Purchase #7 $97.94   3.616%   $101.4815   $101.48   $101.50   $101.50  
  7 purchase totals = $900.59       $986.4877   $986.49   $986.45   $986.40