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 $210.43   10.582%   $232.6977   $232.70   $232.70   $232.70  
  Purchase #2 $60.76   9.155%   $66.3226   $66.32   $66.30   $66.30  
  Purchase #3 $93.89   11.805%   $104.9737   $104.97   $104.95   $105.00  
  Purchase #4 $150.87   7.499%   $162.1837   $162.18   $162.20   $162.20  
  Purchase #5 $231.74   7.128%   $248.2584   $248.26   $248.25   $248.30  
  Purchase #6 $24.32   6.873%   $25.9915   $25.99   $26.00   $26.00  
  Purchase #7 $111.68   12.579%   $125.7282   $125.73   $125.75   $125.70  
  7 purchase totals = $883.69       $966.1558   $966.15   $966.15   $966.20