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 $59.68   13.243%   $67.5834   $67.58   $67.60   $67.60  
  Purchase #2 $29.99   4.113%   $31.2235   $31.22   $31.20   $31.20  
  Purchase #3 $217.76   13.148%   $246.3911   $246.39   $246.40   $246.40  
  Purchase #4 $140.34   6.734%   $149.7905   $149.79   $149.80   $149.80  
  Purchase #5 $27.25   6.295%   $28.9654   $28.97   $28.95   $29.00  
  Purchase #6 $142.25   8.218%   $153.9401   $153.94   $153.95   $153.90  
  Purchase #7 $55.86   7.424%   $60.007   $60.01   $60.00   $60.00  
  7 purchase totals = $673.13       $737.9010   $737.90   $737.90   $737.90