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 $207.86   8.607%   $225.7505   $225.75   $225.75   $225.80  
  Purchase #2 $104.29   5.727%   $110.2627   $110.26   $110.25   $110.30  
  Purchase #3 $103.53   4.604%   $108.2965   $108.30   $108.30   $108.30  
  Purchase #4 $63.85   10.659%   $70.6558   $70.66   $70.65   $70.70  
  Purchase #5 $53.87   5.600%   $56.8867   $56.89   $56.90   $56.90  
  Purchase #6 $202.77   11.274%   $225.6303   $225.63   $225.65   $225.60  
  Purchase #7 $63.45   5.296%   $66.8103   $66.81   $66.80   $66.80  
  7 purchase totals = $799.62       $864.2928   $864.30   $864.30   $864.40