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 $246.72   5.718%   $260.8274   $260.83   $260.85   $260.80  
  Purchase #2 $208.29   12.508%   $234.3429   $234.34   $234.35   $234.30  
  Purchase #3 $183.69   9.589%   $201.304   $201.30   $201.30   $201.30  
  Purchase #4 $83.73   5.297%   $88.1652   $88.17   $88.15   $88.20  
  Purchase #5 $6.81   6.441%   $7.2486   $7.25   $7.25   $7.20  
  Purchase #6 $96.95   8.305%   $105.0017   $105.00   $105.00   $105.00  
  Purchase #7 $82.40   5.542%   $86.9666   $86.97   $86.95   $87.00  
  7 purchase totals = $908.59       $983.8564   $983.86   $983.85   $983.80