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 $192.65   8.397%   $208.8268   $208.83   $208.85   $208.80  
  Purchase #2 $64.92   6.304%   $69.0126   $69.01   $69.00   $69.00  
  Purchase #3 $228.75   6.673%   $244.0145   $244.01   $244.00   $244.00  
  Purchase #4 $233.28   6.228%   $247.8087   $247.81   $247.80   $247.80  
  Purchase #5 $141.57   12.407%   $159.1346   $159.13   $159.15   $159.10  
  Purchase #6 $120.31   8.311%   $130.309   $130.31   $130.30   $130.30  
  Purchase #7 $13.40   13.138%   $15.1605   $15.16   $15.15   $15.20  
  7 purchase totals = $994.88       $1,074.2667   $1,074.26   $1,074.25   $1,074.20