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 $207.92   5.797%   $219.9731   $219.97   $219.95   $220.00  
  Purchase #2 $219.63   12.747%   $247.6262   $247.63   $247.65   $247.60  
  Purchase #3 $48.26   7.717%   $51.9842   $51.98   $52.00   $52.00  
  Purchase #4 $35.63   6.392%   $37.9075   $37.91   $37.90   $37.90  
  Purchase #5 $95.43   4.685%   $99.9009   $99.90   $99.90   $99.90  
  Purchase #6 $148.64   8.110%   $160.6947   $160.69   $160.70   $160.70  
  Purchase #7 $239.34   4.291%   $249.6101   $249.61   $249.60   $249.60  
  7 purchase totals = $994.85       $1,067.6967   $1,067.69   $1,067.70   $1,067.70