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 $34.36   10.466%   $37.9561   $37.96   $37.95   $38.00  
  Purchase #2 $112.81   9.679%   $123.7289   $123.73   $123.75   $123.70  
  Purchase #3 $60.65   8.356%   $65.7179   $65.72   $65.70   $65.70  
  Purchase #4 $185.82   3.656%   $192.6136   $192.61   $192.60   $192.60  
  Purchase #5 $167.79   9.565%   $183.8391   $183.84   $183.85   $183.80  
  Purchase #6 $95.72   4.458%   $99.9872   $99.99   $100.00   $100.00  
  Purchase #7 $234.69   11.167%   $260.8978   $260.90   $260.90   $260.90  
  7 purchase totals = $891.84       $964.7406   $964.75   $964.75   $964.70