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 $41.61   7.507%   $44.7337   $44.73   $44.75   $44.70  
  Purchase #2 $166.92   12.322%   $187.4879   $187.49   $187.50   $187.50  
  Purchase #3 $170.34   3.176%   $175.75   $175.75   $175.75   $175.80  
  Purchase #4 $246.74   11.225%   $274.4366   $274.44   $274.45   $274.40  
  Purchase #5 $94.77   13.118%   $107.2019   $107.20   $107.20   $107.20  
  Purchase #6 $141.77   12.227%   $159.1042   $159.10   $159.10   $159.10  
  Purchase #7 $121.42   7.619%   $130.671   $130.67   $130.65   $130.70  
  7 purchase totals = $983.57       $1,079.3853   $1,079.38   $1,079.40   $1,079.40