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 $189.89   6.644%   $202.5063   $202.51   $202.50   $202.50  
  Purchase #2 $81.53   4.555%   $85.2437   $85.24   $85.25   $85.20  
  Purchase #3 $126.53   6.859%   $135.2087   $135.21   $135.20   $135.20  
  Purchase #4 $235.63   5.227%   $247.9464   $247.95   $247.95   $247.90  
  Purchase #5 $19.83   13.839%   $22.5743   $22.57   $22.55   $22.60  
  Purchase #6 $180.31   3.824%   $187.2051   $187.21   $187.20   $187.20  
  Purchase #7 $15.41   12.854%   $17.3908   $17.39   $17.40   $17.40  
  7 purchase totals = $849.13       $898.0753   $898.08   $898.05   $898.00