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 $245.36   7.282%   $263.2271   $263.23   $263.25   $263.20  
  Purchase #2 $63.99   12.819%   $72.1929   $72.19   $72.20   $72.20  
  Purchase #3 $119.52   5.394%   $125.9669   $125.97   $125.95   $126.00  
  Purchase #4 $190.71   5.617%   $201.4222   $201.42   $201.40   $201.40  
  Purchase #5 $82.91   8.639%   $90.0726   $90.07   $90.05   $90.10  
  Purchase #6 $76.85   3.762%   $79.7411   $79.74   $79.75   $79.70  
  Purchase #7 $168.67   6.215%   $179.1528   $179.15   $179.15   $179.20  
  7 purchase totals = $948.01       $1,011.7756   $1,011.77   $1,011.75   $1,011.80