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 $116.49   8.775%   $126.712   $126.71   $126.70   $126.70  
  Purchase #2 $108.93   13.733%   $123.8894   $123.89   $123.90   $123.90  
  Purchase #3 $91.47   13.790%   $104.0837   $104.08   $104.10   $104.10  
  Purchase #4 $185.96   9.609%   $203.8289   $203.83   $203.85   $203.80  
  Purchase #5 $34.49   7.267%   $36.9964   $37.00   $37.00   $37.00  
  Purchase #6 $27.80   8.608%   $30.193   $30.19   $30.20   $30.20  
  Purchase #7 $240.36   11.483%   $267.9605   $267.96   $267.95   $268.00  
  7 purchase totals = $805.50       $893.6639   $893.66   $893.70   $893.70