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 $62.28   9.596%   $68.2564   $68.26   $68.25   $68.30  
  Purchase #2 $92.50   4.504%   $96.6662   $96.67   $96.65   $96.70  
  Purchase #3 $222.72   6.754%   $237.7625   $237.76   $237.75   $237.80  
  Purchase #4 $11.35   8.671%   $12.3342   $12.33   $12.35   $12.30  
  Purchase #5 $64.69   10.119%   $71.236   $71.24   $71.25   $71.20  
  Purchase #6 $151.40   11.174%   $168.3174   $168.32   $168.30   $168.30  
  Purchase #7 $90.57   5.383%   $95.4454   $95.45   $95.45   $95.40  
  7 purchase totals = $695.51       $750.0181   $750.03   $750.00   $750.00