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 $234.90   10.245%   $258.9655   $258.97   $258.95   $259.00  
  Purchase #2 $231.48   6.566%   $246.679   $246.68   $246.70   $246.70  
  Purchase #3 $155.79   3.581%   $161.3688   $161.37   $161.35   $161.40  
  Purchase #4 $14.29   9.618%   $15.6644   $15.66   $15.65   $15.70  
  Purchase #5 $249.72   7.650%   $268.8236   $268.82   $268.80   $268.80  
  Purchase #6 $49.55   11.674%   $55.3345   $55.33   $55.35   $55.30  
  Purchase #7 $54.53   11.684%   $60.9013   $60.90   $60.90   $60.90  
  7 purchase totals = $990.26       $1,067.7371   $1,067.73   $1,067.70   $1,067.80