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 $57.46   10.150%   $63.2922   $63.29   $63.30   $63.30  
  Purchase #2 $244.71   9.247%   $267.3383   $267.34   $267.35   $267.30  
  Purchase #3 $126.70   3.854%   $131.583   $131.58   $131.60   $131.60  
  Purchase #4 $61.65   10.113%   $67.8847   $67.88   $67.90   $67.90  
  Purchase #5 $60.96   13.163%   $68.9842   $68.98   $69.00   $69.00  
  Purchase #6 $128.28   10.674%   $141.9726   $141.97   $141.95   $142.00  
  Purchase #7 $15.49   5.417%   $16.3291   $16.33   $16.35   $16.30  
  7 purchase totals = $695.25       $757.3841   $757.37   $757.45   $757.40