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 $246.61   9.189%   $269.271   $269.27   $269.25   $269.30  
  Purchase #2 $211.87   5.710%   $223.9678   $223.97   $223.95   $224.00  
  Purchase #3 $218.71   6.170%   $232.2044   $232.20   $232.20   $232.20  
  Purchase #4 $165.89   4.296%   $173.0166   $173.02   $173.00   $173.00  
  Purchase #5 $169.31   3.303%   $174.9023   $174.90   $174.90   $174.90  
  Purchase #6 $49.78   3.674%   $51.6089   $51.61   $51.60   $51.60  
  Purchase #7 $6.69   8.535%   $7.261   $7.26   $7.25   $7.30  
  7 purchase totals = $1,068.86       $1,132.2320   $1,132.23   $1,132.15   $1,132.30