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 $140.84   13.620%   $160.0224   $160.02   $160.00   $160.00  
  Purchase #2 $215.98   9.321%   $236.1115   $236.11   $236.10   $236.10  
  Purchase #3 $235.55   4.812%   $246.8847   $246.88   $246.90   $246.90  
  Purchase #4 $162.64   7.291%   $174.4981   $174.50   $174.50   $174.50  
  Purchase #5 $233.55   7.335%   $250.6809   $250.68   $250.70   $250.70  
  Purchase #6 $170.55   7.113%   $182.6812   $182.68   $182.70   $182.70  
  Purchase #7 $129.68   9.771%   $142.351   $142.35   $142.35   $142.40  
  7 purchase totals = $1,288.79       $1,393.2298   $1,393.22   $1,393.25   $1,393.30