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 $213.98   8.433%   $232.0249   $232.02   $232.00   $232.00  
  Purchase #2 $163.65   11.539%   $182.5336   $182.53   $182.55   $182.50  
  Purchase #3 $76.26   5.861%   $80.7296   $80.73   $80.75   $80.70  
  Purchase #4 $52.77   6.599%   $56.2523   $56.25   $56.25   $56.30  
  Purchase #5 $27.33   13.284%   $30.9605   $30.96   $30.95   $31.00  
  Purchase #6 $29.57   5.388%   $31.1632   $31.16   $31.15   $31.20  
  Purchase #7 $124.42   5.125%   $130.7965   $130.80   $130.80   $130.80  
  7 purchase totals = $687.98       $744.4606   $744.45   $744.45   $744.50