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 $221.97   10.668%   $245.6498   $245.65   $245.65   $245.60  
  Purchase #2 $11.64   6.571%   $12.4049   $12.40   $12.40   $12.40  
  Purchase #3 $195.66   6.330%   $208.0453   $208.05   $208.05   $208.00  
  Purchase #4 $155.65   11.792%   $174.0042   $174.00   $174.00   $174.00  
  Purchase #5 $101.43   4.337%   $105.829   $105.83   $105.85   $105.80  
  Purchase #6 $247.53   9.282%   $270.5057   $270.51   $270.50   $270.50  
  Purchase #7 $222.53   6.127%   $236.1644   $236.16   $236.15   $236.20  
  7 purchase totals = $1,156.41       $1,252.6033   $1,252.60   $1,252.60   $1,252.50