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 $49.59   12.404%   $55.7411   $55.74   $55.75   $55.70  
  Purchase #2 $65.49   10.402%   $72.3023   $72.30   $72.30   $72.30  
  Purchase #3 $196.38   3.791%   $203.8248   $203.82   $203.80   $203.80  
  Purchase #4 $94.48   3.781%   $98.0523   $98.05   $98.05   $98.10  
  Purchase #5 $250.66   10.342%   $276.5833   $276.58   $276.60   $276.60  
  Purchase #6 $106.79   11.544%   $119.1178   $119.12   $119.10   $119.10  
  Purchase #7 $170.80   9.219%   $186.5461   $186.55   $186.55   $186.50  
  7 purchase totals = $934.19       $1,012.1677   $1,012.16   $1,012.15   $1,012.10