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 $152.93   7.637%   $164.6093   $164.61   $164.60   $164.60  
  Purchase #2 $133.86   9.638%   $146.7614   $146.76   $146.75   $146.80  
  Purchase #3 $17.84   7.812%   $19.2337   $19.23   $19.25   $19.20  
  Purchase #4 $217.81   3.649%   $225.7579   $225.76   $225.75   $225.80  
  Purchase #5 $173.85   11.642%   $194.0896   $194.09   $194.10   $194.10  
  Purchase #6 $59.25   9.163%   $64.6791   $64.68   $64.70   $64.70  
  Purchase #7 $164.58   13.381%   $186.6024   $186.60   $186.60   $186.60  
  7 purchase totals = $920.12       $1,001.7334   $1,001.73   $1,001.75   $1,001.80