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 $156.86   4.303%   $163.6097   $163.61   $163.60   $163.60  
  Purchase #2 $241.96   4.497%   $252.8409   $252.84   $252.85   $252.80  
  Purchase #3 $12.29   11.640%   $13.7206   $13.72   $13.70   $13.70  
  Purchase #4 $182.87   9.451%   $200.153   $200.15   $200.15   $200.20  
  Purchase #5 $212.83   4.447%   $222.2946   $222.29   $222.30   $222.30  
  Purchase #6 $77.56   11.573%   $86.536   $86.54   $86.55   $86.50  
  Purchase #7 $26.74   4.591%   $27.9676   $27.97   $27.95   $28.00  
  7 purchase totals = $911.11       $967.1224   $967.12   $967.10   $967.10