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 $67.36   13.623%   $76.5365   $76.54   $76.55   $76.50  
  Purchase #2 $110.40   11.178%   $122.7405   $122.74   $122.75   $122.70  
  Purchase #3 $91.30   8.108%   $98.7026   $98.70   $98.70   $98.70  
  Purchase #4 $139.47   3.148%   $143.8605   $143.86   $143.85   $143.90  
  Purchase #5 $155.64   10.159%   $171.4515   $171.45   $171.45   $171.50  
  Purchase #6 $236.84   3.443%   $244.9944   $244.99   $245.00   $245.00  
  Purchase #7 $5.60   10.785%   $6.204   $6.20   $6.20   $6.20  
  7 purchase totals = $806.61       $864.4900   $864.48   $864.50   $864.50