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 $65.82   12.828%   $74.2634   $74.26   $74.25   $74.30  
  Purchase #2 $122.87   13.540%   $139.5066   $139.51   $139.50   $139.50  
  Purchase #3 $171.68   3.226%   $177.2184   $177.22   $177.20   $177.20  
  Purchase #4 $123.36   10.142%   $135.8712   $135.87   $135.85   $135.90  
  Purchase #5 $188.94   6.109%   $200.4823   $200.48   $200.50   $200.50  
  Purchase #6 $100.60   5.392%   $106.0244   $106.02   $106.00   $106.00  
  Purchase #7 $123.47   7.409%   $132.6179   $132.62   $132.60   $132.60  
  7 purchase totals = $896.74       $965.9842   $965.98   $965.90   $966.00