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 $55.33   11.278%   $61.5701   $61.57   $61.55   $61.60  
  Purchase #2 $238.65   10.259%   $263.1331   $263.13   $263.15   $263.10  
  Purchase #3 $64.71   6.264%   $68.7634   $68.76   $68.75   $68.80  
  Purchase #4 $195.79   11.616%   $218.533   $218.53   $218.55   $218.50  
  Purchase #5 $38.97   3.290%   $40.2521   $40.25   $40.25   $40.30  
  Purchase #6 $83.94   10.659%   $92.8872   $92.89   $92.90   $92.90  
  Purchase #7 $146.64   9.850%   $161.084   $161.08   $161.10   $161.10  
  7 purchase totals = $824.03       $906.2229   $906.21   $906.25   $906.30