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 $110.75   7.220%   $118.7462   $118.75   $118.75   $118.70  
  Purchase #2 $246.27   7.118%   $263.7995   $263.80   $263.80   $263.80  
  Purchase #3 $114.46   4.163%   $119.225   $119.23   $119.25   $119.20  
  Purchase #4 $49.60   11.207%   $55.1587   $55.16   $55.15   $55.20  
  Purchase #5 $60.53   13.533%   $68.7215   $68.72   $68.70   $68.70  
  Purchase #6 $217.57   10.139%   $239.6294   $239.63   $239.65   $239.60  
  Purchase #7 $78.39   7.435%   $84.2183   $84.22   $84.20   $84.20  
  7 purchase totals = $877.57       $949.4986   $949.51   $949.50   $949.40