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 $226.29   11.672%   $252.7026   $252.70   $252.70   $252.70  
  Purchase #2 $119.39   13.168%   $135.1113   $135.11   $135.10   $135.10  
  Purchase #3 $42.43   13.119%   $47.9964   $48.00   $48.00   $48.00  
  Purchase #4 $210.30   8.115%   $227.3658   $227.37   $227.35   $227.40  
  Purchase #5 $151.60   9.376%   $165.814   $165.81   $165.80   $165.80  
  Purchase #6 $53.60   6.391%   $57.0256   $57.03   $57.05   $57.00  
  Purchase #7 $214.78   3.121%   $221.4833   $221.48   $221.50   $221.50  
  7 purchase totals = $1,018.39       $1,107.4990   $1,107.50   $1,107.50   $1,107.50