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 $183.53   11.705%   $205.0122   $205.01   $205.00   $205.00  
  Purchase #2 $50.80   11.733%   $56.7604   $56.76   $56.75   $56.80  
  Purchase #3 $223.89   8.564%   $243.0639   $243.06   $243.05   $243.10  
  Purchase #4 $153.43   12.734%   $172.9678   $172.97   $172.95   $173.00  
  Purchase #5 $230.80   12.327%   $259.2507   $259.25   $259.25   $259.30  
  Purchase #6 $197.62   10.553%   $218.4748   $218.47   $218.45   $218.50  
  Purchase #7 $233.73   5.558%   $246.7207   $246.72   $246.70   $246.70  
  7 purchase totals = $1,273.80       $1,402.2505   $1,402.24   $1,402.15   $1,402.40