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 $233.86   13.475%   $265.3726   $265.37   $265.35   $265.40  
  Purchase #2 $207.92   9.149%   $226.9426   $226.94   $226.95   $226.90  
  Purchase #3 $16.67   7.850%   $17.9786   $17.98   $18.00   $18.00  
  Purchase #4 $23.68   3.194%   $24.4363   $24.44   $24.45   $24.40  
  Purchase #5 $67.91   7.460%   $72.9761   $72.98   $73.00   $73.00  
  Purchase #6 $64.69   13.284%   $73.2834   $73.28   $73.30   $73.30  
  Purchase #7 $83.45   11.657%   $93.1778   $93.18   $93.20   $93.20  
  7 purchase totals = $698.18       $774.1674   $774.17   $774.25   $774.20