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 $250.64   13.303%   $283.9826   $283.98   $284.00   $284.00  
  Purchase #2 $74.25   11.287%   $82.6306   $82.63   $82.65   $82.60  
  Purchase #3 $175.47   12.687%   $197.7319   $197.73   $197.75   $197.70  
  Purchase #4 $229.49   3.481%   $237.4785   $237.48   $237.50   $237.50  
  Purchase #5 $173.69   11.315%   $193.343   $193.34   $193.35   $193.30  
  Purchase #6 $31.61   7.639%   $34.0247   $34.02   $34.00   $34.00  
  Purchase #7 $116.88   4.266%   $121.8661   $121.87   $121.85   $121.90  
  7 purchase totals = $1,052.03       $1,151.0574   $1,151.05   $1,151.10   $1,151.00