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 $36.49   3.292%   $37.6913   $37.69   $37.70   $37.70  
  Purchase #2 $95.25   10.156%   $104.9236   $104.92   $104.90   $104.90  
  Purchase #3 $37.87   12.480%   $42.5962   $42.60   $42.60   $42.60  
  Purchase #4 $198.56   10.533%   $219.4743   $219.47   $219.45   $219.50  
  Purchase #5 $72.49   8.616%   $78.7357   $78.74   $78.75   $78.70  
  Purchase #6 $8.84   11.668%   $9.8715   $9.87   $9.85   $9.90  
  Purchase #7 $182.48   11.153%   $202.832   $202.83   $202.85   $202.80  
  7 purchase totals = $631.98       $696.1246   $696.12   $696.10   $696.10