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 $55.84   7.646%   $60.1095   $60.11   $60.10   $60.10  
  Purchase #2 $49.36   6.269%   $52.4544   $52.45   $52.45   $52.50  
  Purchase #3 $250.60   3.780%   $260.0727   $260.07   $260.05   $260.10  
  Purchase #4 $87.32   11.305%   $97.1915   $97.19   $97.20   $97.20  
  Purchase #5 $98.65   5.349%   $103.9268   $103.93   $103.95   $103.90  
  Purchase #6 $176.32   12.813%   $198.9119   $198.91   $198.90   $198.90  
  Purchase #7 $10.93   3.568%   $11.32   $11.32   $11.30   $11.30  
  7 purchase totals = $729.02       $783.9868   $783.98   $783.95   $784.00