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 $54.76   11.380%   $60.9917   $60.99   $61.00   $61.00  
  Purchase #2 $200.49   7.293%   $215.1117   $215.11   $215.10   $215.10  
  Purchase #3 $149.97   3.150%   $154.6941   $154.69   $154.70   $154.70  
  Purchase #4 $98.68   7.199%   $105.784   $105.78   $105.80   $105.80  
  Purchase #5 $49.87   3.605%   $51.6678   $51.67   $51.65   $51.70  
  Purchase #6 $119.86   3.834%   $124.4554   $124.46   $124.45   $124.50  
  Purchase #7 $225.81   3.350%   $233.3746   $233.37   $233.35   $233.40  
  7 purchase totals = $899.44       $946.0793   $946.07   $946.05   $946.20