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 $67.37   3.648%   $69.8277   $69.83   $69.85   $69.80  
  Purchase #2 $250.55   3.782%   $260.0258   $260.03   $260.05   $260.00  
  Purchase #3 $169.90   13.450%   $192.7516   $192.75   $192.75   $192.80  
  Purchase #4 $226.36   9.775%   $248.4867   $248.49   $248.50   $248.50  
  Purchase #5 $42.39   4.582%   $44.3323   $44.33   $44.35   $44.30  
  Purchase #6 $10.91   12.474%   $12.2709   $12.27   $12.25   $12.30  
  Purchase #7 $175.40   10.718%   $194.1994   $194.20   $194.20   $194.20  
  7 purchase totals = $942.88       $1,021.8944   $1,021.90   $1,021.95   $1,021.90