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 $30.64   12.128%   $34.356   $34.36   $34.35   $34.40  
  Purchase #2 $180.96   7.215%   $194.0163   $194.02   $194.00   $194.00  
  Purchase #3 $88.67   10.415%   $97.905   $97.91   $97.90   $97.90  
  Purchase #4 $212.51   10.842%   $235.5503   $235.55   $235.55   $235.60  
  Purchase #5 $81.77   10.434%   $90.3019   $90.30   $90.30   $90.30  
  Purchase #6 $228.40   13.666%   $259.6131   $259.61   $259.60   $259.60  
  Purchase #7 $62.42   6.119%   $66.2395   $66.24   $66.25   $66.20  
  7 purchase totals = $885.37       $977.9821   $977.99   $977.95   $978.00