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 $64.54   3.104%   $66.5433   $66.54   $66.55   $66.50  
  Purchase #2 $63.46   11.447%   $70.7243   $70.72   $70.70   $70.70  
  Purchase #3 $193.61   7.785%   $208.6825   $208.68   $208.70   $208.70  
  Purchase #4 $225.60   10.118%   $248.4262   $248.43   $248.45   $248.40  
  Purchase #5 $91.60   13.735%   $104.1813   $104.18   $104.20   $104.20  
  Purchase #6 $174.57   13.109%   $197.4544   $197.45   $197.45   $197.50  
  Purchase #7 $110.26   10.445%   $121.7767   $121.78   $121.80   $121.80  
  7 purchase totals = $923.64       $1,017.7887   $1,017.78   $1,017.85   $1,017.80