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 $213.85   9.242%   $233.614   $233.61   $233.60   $233.60  
  Purchase #2 $59.95   9.341%   $65.5499   $65.55   $65.55   $65.50  
  Purchase #3 $105.25   11.584%   $117.4422   $117.44   $117.45   $117.40  
  Purchase #4 $226.66   6.319%   $240.9826   $240.98   $241.00   $241.00  
  Purchase #5 $171.51   8.346%   $185.8242   $185.82   $185.80   $185.80  
  Purchase #6 $203.95   5.854%   $215.8892   $215.89   $215.90   $215.90  
  Purchase #7 $138.63   6.129%   $147.1266   $147.13   $147.15   $147.10  
  7 purchase totals = $1,119.80       $1,206.4287   $1,206.42   $1,206.45   $1,206.30