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 $71.86   6.783%   $76.7343   $76.73   $76.75   $76.70  
  Purchase #2 $33.59   8.340%   $36.3914   $36.39   $36.40   $36.40  
  Purchase #3 $41.64   7.232%   $44.6514   $44.65   $44.65   $44.70  
  Purchase #4 $214.79   9.106%   $234.3488   $234.35   $234.35   $234.30  
  Purchase #5 $40.63   8.698%   $44.164   $44.16   $44.15   $44.20  
  Purchase #6 $167.60   9.781%   $183.993   $183.99   $184.00   $184.00  
  Purchase #7 $30.38   13.619%   $34.5175   $34.52   $34.50   $34.50  
  7 purchase totals = $600.49       $654.8004   $654.79   $654.80   $654.80