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 $220.60   9.261%   $241.0298   $241.03   $241.05   $241.00  
  Purchase #2 $97.61   7.540%   $104.9698   $104.97   $104.95   $105.00  
  Purchase #3 $100.49   7.126%   $107.6509   $107.65   $107.65   $107.70  
  Purchase #4 $222.25   6.542%   $236.7896   $236.79   $236.80   $236.80  
  Purchase #5 $69.93   6.287%   $74.3265   $74.33   $74.35   $74.30  
  Purchase #6 $21.62   5.803%   $22.8746   $22.87   $22.85   $22.90  
  Purchase #7 $115.37   12.330%   $129.5951   $129.60   $129.60   $129.60  
  7 purchase totals = $847.87       $917.2363   $917.24   $917.25   $917.30