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 $187.36   10.106%   $206.2946   $206.29   $206.30   $206.30  
  Purchase #2 $235.59   11.785%   $263.3543   $263.35   $263.35   $263.40  
  Purchase #3 $62.58   10.182%   $68.9519   $68.95   $68.95   $69.00  
  Purchase #4 $54.93   8.630%   $59.6705   $59.67   $59.65   $59.70  
  Purchase #5 $148.34   8.576%   $161.0616   $161.06   $161.05   $161.10  
  Purchase #6 $200.47   10.524%   $221.5675   $221.57   $221.55   $221.60  
  Purchase #7 $243.38   13.132%   $275.3407   $275.34   $275.35   $275.30  
  7 purchase totals = $1,132.65       $1,256.2411   $1,256.23   $1,256.20   $1,256.40