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 $188.47   9.292%   $205.9826   $205.98   $206.00   $206.00  
  Purchase #2 $167.59   11.733%   $187.2533   $187.25   $187.25   $187.30  
  Purchase #3 $188.28   5.542%   $198.7145   $198.71   $198.70   $198.70  
  Purchase #4 $250.48   10.480%   $276.7303   $276.73   $276.75   $276.70  
  Purchase #5 $90.91   12.511%   $102.2838   $102.28   $102.30   $102.30  
  Purchase #6 $19.52   13.163%   $22.0894   $22.09   $22.10   $22.10  
  Purchase #7 $53.42   6.507%   $56.896   $56.90   $56.90   $56.90  
  7 purchase totals = $958.67       $1,049.9499   $1,049.94   $1,050.00   $1,050.00