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 $243.65   5.772%   $257.7135   $257.71   $257.70   $257.70  
  Purchase #2 $224.83   9.695%   $246.6273   $246.63   $246.65   $246.60  
  Purchase #3 $58.32   13.754%   $66.3413   $66.34   $66.35   $66.30  
  Purchase #4 $116.38   7.347%   $124.9304   $124.93   $124.95   $124.90  
  Purchase #5 $33.40   9.462%   $36.5603   $36.56   $36.55   $36.60  
  Purchase #6 $73.25   12.237%   $82.2136   $82.21   $82.20   $82.20  
  Purchase #7 $196.68   11.516%   $219.3297   $219.33   $219.35   $219.30  
  7 purchase totals = $946.51       $1,033.7161   $1,033.71   $1,033.75   $1,033.60