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 $118.81   7.316%   $127.5021   $127.50   $127.50   $127.50  
  Purchase #2 $211.57   11.766%   $236.4633   $236.46   $236.45   $236.50  
  Purchase #3 $209.28   7.346%   $224.6537   $224.65   $224.65   $224.70  
  Purchase #4 $235.60   13.553%   $267.5309   $267.53   $267.55   $267.50  
  Purchase #5 $130.39   8.571%   $141.5657   $141.57   $141.55   $141.60  
  Purchase #6 $53.30   10.619%   $58.9599   $58.96   $58.95   $59.00  
  Purchase #7 $230.35   10.209%   $253.8664   $253.87   $253.85   $253.90  
  7 purchase totals = $1,189.30       $1,310.5420   $1,310.54   $1,310.50   $1,310.70