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 $50.55   6.767%   $53.9707   $53.97   $53.95   $54.00  
  Purchase #2 $223.38   6.556%   $238.0248   $238.02   $238.00   $238.00  
  Purchase #3 $102.99   7.667%   $110.8862   $110.89   $110.90   $110.90  
  Purchase #4 $41.63   12.667%   $46.9033   $46.90   $46.90   $46.90  
  Purchase #5 $120.55   8.253%   $130.499   $130.50   $130.50   $130.50  
  Purchase #6 $16.43   13.172%   $18.5942   $18.59   $18.60   $18.60  
  Purchase #7 $14.85   8.759%   $16.1507   $16.15   $16.15   $16.20  
  7 purchase totals = $570.38       $615.0289   $615.02   $615.00   $615.10