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 $118.54   6.654%   $126.4277   $126.43   $126.45   $126.40  
  Purchase #2 $45.85   6.433%   $48.7995   $48.80   $48.80   $48.80  
  Purchase #3 $91.99   5.395%   $96.9529   $96.95   $96.95   $97.00  
  Purchase #4 $242.26   4.786%   $253.8546   $253.85   $253.85   $253.90  
  Purchase #5 $60.45   10.460%   $66.7731   $66.77   $66.75   $66.80  
  Purchase #6 $44.85   6.463%   $47.7487   $47.75   $47.75   $47.70  
  Purchase #7 $26.41   10.188%   $29.1007   $29.10   $29.10   $29.10  
  7 purchase totals = $630.35       $669.6572   $669.65   $669.65   $669.70