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 $222.82   4.797%   $233.5087   $233.51   $233.50   $233.50  
  Purchase #2 $164.44   6.272%   $174.7537   $174.75   $174.75   $174.80  
  Purchase #3 $50.62   7.348%   $54.3396   $54.34   $54.35   $54.30  
  Purchase #4 $232.93   8.321%   $252.3121   $252.31   $252.30   $252.30  
  Purchase #5 $116.74   4.475%   $121.9641   $121.96   $121.95   $122.00  
  Purchase #6 $107.76   3.594%   $111.6329   $111.63   $111.65   $111.60  
  Purchase #7 $61.27   7.509%   $65.8708   $65.87   $65.85   $65.90  
  7 purchase totals = $956.58       $1,014.3819   $1,014.37   $1,014.35   $1,014.40