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 $169.38   9.716%   $185.837   $185.84   $185.85   $185.80  
  Purchase #2 $246.74   12.134%   $276.6794   $276.68   $276.70   $276.70  
  Purchase #3 $235.26   8.643%   $255.5935   $255.59   $255.60   $255.60  
  Purchase #4 $41.29   8.127%   $44.6456   $44.65   $44.65   $44.60  
  Purchase #5 $185.89   12.665%   $209.433   $209.43   $209.45   $209.40  
  Purchase #6 $244.95   8.234%   $265.1192   $265.12   $265.10   $265.10  
  Purchase #7 $162.53   7.287%   $174.3736   $174.37   $174.35   $174.40  
  7 purchase totals = $1,286.04       $1,411.6813   $1,411.68   $1,411.70   $1,411.60