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 $232.81   6.569%   $248.1033   $248.10   $248.10   $248.10  
  Purchase #2 $204.76   5.762%   $216.5583   $216.56   $216.55   $216.60  
  Purchase #3 $197.62   6.106%   $209.6867   $209.69   $209.70   $209.70  
  Purchase #4 $66.92   3.691%   $69.39   $69.39   $69.40   $69.40  
  Purchase #5 $163.32   10.860%   $181.0566   $181.06   $181.05   $181.10  
  Purchase #6 $61.40   5.846%   $64.9894   $64.99   $65.00   $65.00  
  Purchase #7 $194.53   7.694%   $209.4971   $209.50   $209.50   $209.50  
  7 purchase totals = $1,121.36       $1,199.2814   $1,199.29   $1,199.30   $1,199.40