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 $221.51   9.233%   $241.962   $241.96   $241.95   $242.00  
  Purchase #2 $12.35   11.186%   $13.7315   $13.73   $13.75   $13.70  
  Purchase #3 $162.85   8.502%   $176.6955   $176.70   $176.70   $176.70  
  Purchase #4 $55.44   9.515%   $60.7151   $60.72   $60.70   $60.70  
  Purchase #5 $103.26   4.571%   $107.98   $107.98   $108.00   $108.00  
  Purchase #6 $220.95   4.857%   $231.6815   $231.68   $231.70   $231.70  
  Purchase #7 $115.98   3.639%   $120.2005   $120.20   $120.20   $120.20  
  7 purchase totals = $892.34       $952.9661   $952.97   $953.00   $953.00