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 $90.61   7.449%   $97.3595   $97.36   $97.35   $97.40  
  Purchase #2 $83.87   7.710%   $90.3364   $90.34   $90.35   $90.30  
  Purchase #3 $215.49   8.670%   $234.173   $234.17   $234.15   $234.20  
  Purchase #4 $130.90   8.355%   $141.8367   $141.84   $141.85   $141.80  
  Purchase #5 $93.74   4.550%   $98.0052   $98.01   $98.00   $98.00  
  Purchase #6 $232.43   5.690%   $245.6553   $245.66   $245.65   $245.70  
  Purchase #7 $56.83   3.148%   $58.619   $58.62   $58.60   $58.60  
  7 purchase totals = $903.87       $965.9851   $966.00   $965.95   $966.00