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 $55.53   11.243%   $61.7732   $61.77   $61.75   $61.80  
  Purchase #2 $28.31   3.797%   $29.3849   $29.38   $29.40   $29.40  
  Purchase #3 $83.85   12.449%   $94.2885   $94.29   $94.30   $94.30  
  Purchase #4 $23.53   12.620%   $26.4995   $26.50   $26.50   $26.50  
  Purchase #5 $227.55   7.648%   $244.953   $244.95   $244.95   $245.00  
  Purchase #6 $196.80   10.874%   $218.2   $218.20   $218.20   $218.20  
  Purchase #7 $162.26   5.367%   $170.9685   $170.97   $170.95   $171.00  
  7 purchase totals = $777.83       $846.0676   $846.06   $846.05   $846.20