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 $55.53   5.873%   $58.7913   $58.79   $58.80   $58.80  
  Purchase #2 $183.80   6.693%   $196.1017   $196.10   $196.10   $196.10  
  Purchase #3 $240.38   8.298%   $260.3267   $260.33   $260.35   $260.30  
  Purchase #4 $44.60   13.292%   $50.5282   $50.53   $50.55   $50.50  
  Purchase #5 $171.71   13.754%   $195.327   $195.33   $195.35   $195.30  
  Purchase #6 $71.61   6.241%   $76.0792   $76.08   $76.10   $76.10  
  Purchase #7 $54.95   5.161%   $57.786   $57.79   $57.80   $57.80  
  7 purchase totals = $822.58       $894.9401   $894.95   $895.05   $894.90