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 $38.81   13.379%   $44.0024   $44.00   $44.00   $44.00  
  Purchase #2 $68.88   11.217%   $76.6063   $76.61   $76.60   $76.60  
  Purchase #3 $52.79   5.251%   $55.562   $55.56   $55.55   $55.60  
  Purchase #4 $228.45   7.853%   $246.3902   $246.39   $246.40   $246.40  
  Purchase #5 $169.94   7.284%   $182.3184   $182.32   $182.30   $182.30  
  Purchase #6 $137.95   10.331%   $152.2016   $152.20   $152.20   $152.20  
  Purchase #7 $33.25   9.210%   $36.3123   $36.31   $36.30   $36.30  
  7 purchase totals = $730.07       $793.3932   $793.39   $793.35   $793.40