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 $190.29   6.659%   $202.9614   $202.96   $202.95   $203.00  
  Purchase #2 $237.35   10.249%   $261.676   $261.68   $261.70   $261.70  
  Purchase #3 $41.94   9.513%   $45.9298   $45.93   $45.95   $45.90  
  Purchase #4 $81.84   11.687%   $91.4046   $91.40   $91.40   $91.40  
  Purchase #5 $22.48   7.864%   $24.2478   $24.25   $24.25   $24.20  
  Purchase #6 $21.64   8.344%   $23.4456   $23.45   $23.45   $23.40  
  Purchase #7 $191.39   5.215%   $201.371   $201.37   $201.35   $201.40  
  7 purchase totals = $786.93       $851.0362   $851.04   $851.05   $851.00