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 $216.77   8.670%   $235.564   $235.56   $235.55   $235.60  
  Purchase #2 $18.36   3.204%   $18.9483   $18.95   $18.95   $18.90  
  Purchase #3 $190.51   3.596%   $197.3607   $197.36   $197.35   $197.40  
  Purchase #4 $74.50   8.208%   $80.615   $80.62   $80.60   $80.60  
  Purchase #5 $69.78   5.153%   $73.3758   $73.38   $73.40   $73.40  
  Purchase #6 $44.92   3.731%   $46.596   $46.60   $46.60   $46.60  
  Purchase #7 $223.51   10.745%   $247.5261   $247.53   $247.55   $247.50  
  7 purchase totals = $838.35       $899.9859   $900.00   $900.00   $900.00