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 $233.35   10.546%   $257.9591   $257.96   $257.95   $258.00  
  Purchase #2 $174.50   9.522%   $191.1159   $191.12   $191.10   $191.10  
  Purchase #3 $232.74   10.800%   $257.8759   $257.88   $257.90   $257.90  
  Purchase #4 $15.87   6.173%   $16.8497   $16.85   $16.85   $16.80  
  Purchase #5 $234.30   4.140%   $244   $244.00   $244.00   $244.00  
  Purchase #6 $91.38   6.459%   $97.2822   $97.28   $97.30   $97.30  
  Purchase #7 $88.41   6.690%   $94.3246   $94.32   $94.30   $94.30  
  7 purchase totals = $1,070.55       $1,159.4074   $1,159.41   $1,159.40   $1,159.40