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 $227.55   8.652%   $247.2376   $247.24   $247.25   $247.20  
  Purchase #2 $178.64   10.527%   $197.4454   $197.45   $197.45   $197.40  
  Purchase #3 $141.31   13.836%   $160.8617   $160.86   $160.85   $160.90  
  Purchase #4 $216.41   9.177%   $236.2699   $236.27   $236.25   $236.30  
  Purchase #5 $211.40   10.409%   $233.4046   $233.40   $233.40   $233.40  
  Purchase #6 $93.30   4.169%   $97.1897   $97.19   $97.20   $97.20  
  Purchase #7 $38.95   13.250%   $44.1109   $44.11   $44.10   $44.10  
  7 purchase totals = $1,107.56       $1,216.5198   $1,216.52   $1,216.50   $1,216.50