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 $20.91   7.467%   $22.4713   $22.47   $22.45   $22.50  
  Purchase #2 $128.47   4.308%   $134.0045   $134.00   $134.00   $134.00  
  Purchase #3 $15.83   10.864%   $17.5498   $17.55   $17.55   $17.50  
  Purchase #4 $134.78   8.491%   $146.2242   $146.22   $146.20   $146.20  
  Purchase #5 $47.39   9.592%   $51.9356   $51.94   $51.95   $51.90  
  Purchase #6 $126.58   13.767%   $144.0063   $144.01   $144.00   $144.00  
  Purchase #7 $99.88   5.775%   $105.6481   $105.65   $105.65   $105.60  
  7 purchase totals = $573.84       $621.8398   $621.84   $621.80   $621.70