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 $127.67   5.224%   $134.3395   $134.34   $134.35   $134.30  
  Purchase #2 $53.96   4.691%   $56.4913   $56.49   $56.50   $56.50  
  Purchase #3 $183.95   6.830%   $196.5138   $196.51   $196.50   $196.50  
  Purchase #4 $239.63   6.300%   $254.7267   $254.73   $254.75   $254.70  
  Purchase #5 $201.91   5.243%   $212.4961   $212.50   $212.50   $212.50  
  Purchase #6 $107.36   9.773%   $117.8523   $117.85   $117.85   $117.90  
  Purchase #7 $43.56   7.114%   $46.6589   $46.66   $46.65   $46.70  
  7 purchase totals = $958.04       $1,019.0786   $1,019.08   $1,019.10   $1,019.10