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 $47.83   12.808%   $53.9561   $53.96   $53.95   $54.00  
  Purchase #2 $222.48   9.316%   $243.2062   $243.21   $243.20   $243.20  
  Purchase #3 $159.55   11.181%   $177.3893   $177.39   $177.40   $177.40  
  Purchase #4 $84.55   9.864%   $92.89   $92.89   $92.90   $92.90  
  Purchase #5 $35.98   9.144%   $39.27   $39.27   $39.25   $39.30  
  Purchase #6 $248.88   8.250%   $269.4126   $269.41   $269.40   $269.40  
  Purchase #7 $107.55   11.753%   $120.1904   $120.19   $120.20   $120.20  
  7 purchase totals = $906.82       $996.3146   $996.32   $996.30   $996.40