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 $86.55   11.767%   $96.7343   $96.73   $96.75   $96.70  
  Purchase #2 $216.32   5.189%   $227.5448   $227.54   $227.55   $227.50  
  Purchase #3 $220.40   11.184%   $245.0495   $245.05   $245.05   $245.00  
  Purchase #4 $132.66   7.261%   $142.2924   $142.29   $142.30   $142.30  
  Purchase #5 $246.75   6.108%   $261.8215   $261.82   $261.80   $261.80  
  Purchase #6 $36.96   12.495%   $41.5782   $41.58   $41.60   $41.60  
  Purchase #7 $190.29   13.864%   $216.6718   $216.67   $216.65   $216.70  
  7 purchase totals = $1,129.93       $1,231.6925   $1,231.68   $1,231.70   $1,231.60