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 $207.87   9.156%   $226.9026   $226.90   $226.90   $226.90  
  Purchase #2 $59.38   12.531%   $66.8209   $66.82   $66.80   $66.80  
  Purchase #3 $119.69   13.293%   $135.6004   $135.60   $135.60   $135.60  
  Purchase #4 $198.49   8.854%   $216.0643   $216.06   $216.05   $216.10  
  Purchase #5 $146.38   5.142%   $153.9069   $153.91   $153.90   $153.90  
  Purchase #6 $151.85   12.438%   $170.7371   $170.74   $170.75   $170.70  
  Purchase #7 $43.68   6.401%   $46.476   $46.48   $46.50   $46.50  
  7 purchase totals = $927.34       $1,016.5082   $1,016.51   $1,016.50   $1,016.50