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 $60.87   12.328%   $68.3741   $68.37   $68.35   $68.40  
  Purchase #2 $182.69   9.248%   $199.5852   $199.59   $199.60   $199.60  
  Purchase #3 $17.94   5.850%   $18.9895   $18.99   $19.00   $19.00  
  Purchase #4 $236.59   11.225%   $263.1472   $263.15   $263.15   $263.10  
  Purchase #5 $226.71   8.731%   $246.5041   $246.50   $246.50   $246.50  
  Purchase #6 $50.28   6.644%   $53.6206   $53.62   $53.60   $53.60  
  Purchase #7 $110.71   13.365%   $125.5064   $125.51   $125.50   $125.50  
  7 purchase totals = $885.79       $975.7271   $975.73   $975.70   $975.70