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 $23.43   11.383%   $26.097   $26.10   $26.10   $26.10  
  Purchase #2 $193.39   5.174%   $203.396   $203.40   $203.40   $203.40  
  Purchase #3 $167.65   5.266%   $176.4784   $176.48   $176.50   $176.50  
  Purchase #4 $138.26   7.154%   $148.1511   $148.15   $148.15   $148.20  
  Purchase #5 $46.27   8.505%   $50.2053   $50.21   $50.20   $50.20  
  Purchase #6 $246.47   4.566%   $257.7238   $257.72   $257.70   $257.70  
  Purchase #7 $19.37   12.522%   $21.7955   $21.80   $21.80   $21.80  
  7 purchase totals = $834.84       $883.8471   $883.86   $883.85   $883.90