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 $242.30   10.871%   $268.6404   $268.64   $268.65   $268.60  
  Purchase #2 $206.88   12.323%   $232.3738   $232.37   $232.35   $232.40  
  Purchase #3 $192.88   10.330%   $212.8045   $212.80   $212.80   $212.80  
  Purchase #4 $232.30   5.205%   $244.3912   $244.39   $244.40   $244.40  
  Purchase #5 $69.79   7.195%   $74.8114   $74.81   $74.80   $74.80  
  Purchase #6 $114.64   5.806%   $121.296   $121.30   $121.30   $121.30  
  Purchase #7 $145.99   4.589%   $152.6895   $152.69   $152.70   $152.70  
  7 purchase totals = $1,204.78       $1,307.0068   $1,307.00   $1,307.00   $1,307.00