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 $63.71   3.830%   $66.1501   $66.15   $66.15   $66.20  
  Purchase #2 $177.53   11.467%   $197.8874   $197.89   $197.90   $197.90  
  Purchase #3 $190.89   5.194%   $200.8048   $200.80   $200.80   $200.80  
  Purchase #4 $210.30   4.837%   $220.4722   $220.47   $220.45   $220.50  
  Purchase #5 $62.36   10.677%   $69.0182   $69.02   $69.00   $69.00  
  Purchase #6 $208.74   11.493%   $232.7305   $232.73   $232.75   $232.70  
  Purchase #7 $169.36   3.470%   $175.2368   $175.24   $175.25   $175.20  
  7 purchase totals = $1,082.89       $1,162.3000   $1,162.30   $1,162.30   $1,162.30