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 $235.57   12.579%   $265.2024   $265.20   $265.20   $265.20  
  Purchase #2 $145.63   11.804%   $162.8202   $162.82   $162.80   $162.80  
  Purchase #3 $46.53   13.867%   $52.9823   $52.98   $53.00   $53.00  
  Purchase #4 $68.42   4.866%   $71.7493   $71.75   $71.75   $71.70  
  Purchase #5 $209.34   13.369%   $237.3267   $237.33   $237.35   $237.30  
  Purchase #6 $26.61   12.160%   $29.8458   $29.85   $29.85   $29.80  
  Purchase #7 $129.54   3.591%   $134.1918   $134.19   $134.20   $134.20  
  7 purchase totals = $861.64       $954.1185   $954.12   $954.15   $954.00