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 $65.49   4.165%   $68.2177   $68.22   $68.20   $68.20  
  Purchase #2 $240.91   8.843%   $262.2137   $262.21   $262.20   $262.20  
  Purchase #3 $232.56   10.123%   $256.102   $256.10   $256.10   $256.10  
  Purchase #4 $44.27   11.127%   $49.1959   $49.20   $49.20   $49.20  
  Purchase #5 $177.28   10.129%   $195.2367   $195.24   $195.25   $195.20  
  Purchase #6 $62.72   9.126%   $68.4438   $68.44   $68.45   $68.40  
  Purchase #7 $128.73   3.554%   $133.3051   $133.31   $133.30   $133.30  
  7 purchase totals = $951.96       $1,032.7149   $1,032.72   $1,032.70   $1,032.60