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 $30.37   10.308%   $33.5005   $33.50   $33.50   $33.50  
  Purchase #2 $183.57   5.439%   $193.5544   $193.55   $193.55   $193.60  
  Purchase #3 $27.67   4.121%   $28.8103   $28.81   $28.80   $28.80  
  Purchase #4 $125.37   6.429%   $133.43   $133.43   $133.45   $133.40  
  Purchase #5 $56.72   10.739%   $62.8112   $62.81   $62.80   $62.80  
  Purchase #6 $220.63   8.459%   $239.2931   $239.29   $239.30   $239.30  
  Purchase #7 $152.84   5.734%   $161.6038   $161.60   $161.60   $161.60  
  7 purchase totals = $797.17       $853.0033   $852.99   $853.00   $853.00