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 $226.58   8.771%   $246.4533   $246.45   $246.45   $246.50  
  Purchase #2 $205.90   3.147%   $212.3797   $212.38   $212.40   $212.40  
  Purchase #3 $194.35   13.151%   $219.909   $219.91   $219.90   $219.90  
  Purchase #4 $58.60   10.192%   $64.5725   $64.57   $64.55   $64.60  
  Purchase #5 $152.88   13.695%   $173.8169   $173.82   $173.80   $173.80  
  Purchase #6 $241.40   3.650%   $250.2111   $250.21   $250.20   $250.20  
  Purchase #7 $69.56   4.240%   $72.5093   $72.51   $72.50   $72.50  
  7 purchase totals = $1,149.27       $1,239.8518   $1,239.85   $1,239.80   $1,239.90