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 $34.59   10.867%   $38.3489   $38.35   $38.35   $38.30  
  Purchase #2 $68.75   5.621%   $72.6144   $72.61   $72.60   $72.60  
  Purchase #3 $84.30   12.373%   $94.7304   $94.73   $94.75   $94.70  
  Purchase #4 $188.96   3.451%   $195.481   $195.48   $195.50   $195.50  
  Purchase #5 $97.29   10.223%   $107.236   $107.24   $107.25   $107.20  
  Purchase #6 $235.61   8.205%   $254.9418   $254.94   $254.95   $254.90  
  Purchase #7 $241.88   12.716%   $272.6375   $272.64   $272.65   $272.60  
  7 purchase totals = $951.38       $1,035.9900   $1,035.99   $1,036.05   $1,035.80