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 $215.53   13.242%   $244.0705   $244.07   $244.05   $244.10  
  Purchase #2 $119.46   12.820%   $134.7748   $134.77   $134.75   $134.80  
  Purchase #3 $62.64   5.500%   $66.0852   $66.09   $66.10   $66.10  
  Purchase #4 $88.87   6.612%   $94.7461   $94.75   $94.75   $94.70  
  Purchase #5 $208.26   11.584%   $232.3848   $232.38   $232.40   $232.40  
  Purchase #6 $192.50   6.475%   $204.9644   $204.96   $204.95   $205.00  
  Purchase #7 $94.31   4.309%   $98.3738   $98.37   $98.35   $98.40  
  7 purchase totals = $981.57       $1,075.3996   $1,075.39   $1,075.35   $1,075.50