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 $178.99   12.857%   $202.0027   $202.00   $202.00   $202.00  
  Purchase #2 $110.54   5.705%   $116.8463   $116.85   $116.85   $116.80  
  Purchase #3 $231.26   10.458%   $255.4452   $255.45   $255.45   $255.40  
  Purchase #4 $159.74   8.431%   $173.2077   $173.21   $173.20   $173.20  
  Purchase #5 $165.63   11.235%   $184.2385   $184.24   $184.25   $184.20  
  Purchase #6 $200.40   11.533%   $223.5121   $223.51   $223.50   $223.50  
  Purchase #7 $50.61   11.255%   $56.3062   $56.31   $56.30   $56.30  
  7 purchase totals = $1,097.17       $1,211.5587   $1,211.57   $1,211.55   $1,211.40