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 $77.91   6.302%   $82.8199   $82.82   $82.80   $82.80  
  Purchase #2 $134.94   8.314%   $146.1589   $146.16   $146.15   $146.20  
  Purchase #3 $94.62   3.384%   $97.8219   $97.82   $97.80   $97.80  
  Purchase #4 $241.99   6.376%   $257.4193   $257.42   $257.40   $257.40  
  Purchase #5 $68.42   8.171%   $74.0106   $74.01   $74.00   $74.00  
  Purchase #6 $249.46   7.545%   $268.2818   $268.28   $268.30   $268.30  
  Purchase #7 $89.65   11.149%   $99.6451   $99.65   $99.65   $99.60  
  7 purchase totals = $956.99       $1,026.1575   $1,026.16   $1,026.10   $1,026.10