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 $247.91   13.620%   $281.6753   $281.68   $281.70   $281.70  
  Purchase #2 $231.59   6.854%   $247.4632   $247.46   $247.45   $247.50  
  Purchase #3 $47.49   11.554%   $52.977   $52.98   $53.00   $53.00  
  Purchase #4 $143.97   13.189%   $162.9582   $162.96   $162.95   $163.00  
  Purchase #5 $50.73   4.811%   $53.1706   $53.17   $53.15   $53.20  
  Purchase #6 $214.78   5.357%   $226.2858   $226.29   $226.30   $226.30  
  Purchase #7 $7.54   3.638%   $7.8143   $7.81   $7.80   $7.80  
  7 purchase totals = $944.01       $1,032.3444   $1,032.35   $1,032.35   $1,032.50