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 $56.75   12.717%   $63.9669   $63.97   $63.95   $64.00  
  Purchase #2 $5.46   10.300%   $6.0224   $6.02   $6.00   $6.00  
  Purchase #3 $20.80   7.149%   $22.287   $22.29   $22.30   $22.30  
  Purchase #4 $192.73   11.215%   $214.3447   $214.34   $214.35   $214.30  
  Purchase #5 $34.32   9.349%   $37.5286   $37.53   $37.55   $37.50  
  Purchase #6 $167.68   13.770%   $190.7695   $190.77   $190.75   $190.80  
  Purchase #7 $171.44   11.657%   $191.4248   $191.42   $191.40   $191.40  
  7 purchase totals = $649.18       $726.3439   $726.34   $726.30   $726.30