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 $211.37   10.224%   $232.9805   $232.98   $233.00   $233.00  
  Purchase #2 $168.95   13.263%   $191.3578   $191.36   $191.35   $191.40  
  Purchase #3 $10.87   9.601%   $11.9136   $11.91   $11.90   $11.90  
  Purchase #4 $198.45   8.508%   $215.3341   $215.33   $215.35   $215.30  
  Purchase #5 $63.67   5.664%   $67.2763   $67.28   $67.30   $67.30  
  Purchase #6 $125.83   8.477%   $136.4966   $136.50   $136.50   $136.50  
  Purchase #7 $246.76   6.784%   $263.5002   $263.50   $263.50   $263.50  
  7 purchase totals = $1,025.90       $1,118.8591   $1,118.86   $1,118.90   $1,118.90