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 $90.67   6.598%   $96.6524   $96.65   $96.65   $96.70  
  Purchase #2 $212.65   12.669%   $239.5906   $239.59   $239.60   $239.60  
  Purchase #3 $109.30   7.658%   $117.6702   $117.67   $117.65   $117.70  
  Purchase #4 $192.54   8.257%   $208.438   $208.44   $208.45   $208.40  
  Purchase #5 $192.61   12.607%   $216.8923   $216.89   $216.90   $216.90  
  Purchase #6 $161.98   6.716%   $172.8586   $172.86   $172.85   $172.90  
  Purchase #7 $155.58   7.364%   $167.0369   $167.04   $167.05   $167.00  
  7 purchase totals = $1,115.33       $1,219.1390   $1,219.14   $1,219.15   $1,219.20