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 $193.33   4.194%   $201.4383   $201.44   $201.45   $201.40  
  Purchase #2 $24.25   8.202%   $26.239   $26.24   $26.25   $26.20  
  Purchase #3 $120.48   6.170%   $127.9136   $127.91   $127.90   $127.90  
  Purchase #4 $102.33   13.305%   $115.945   $115.95   $115.95   $115.90  
  Purchase #5 $18.44   3.270%   $19.043   $19.04   $19.05   $19.00  
  Purchase #6 $100.48   8.161%   $108.6802   $108.68   $108.70   $108.70  
  Purchase #7 $154.27   6.250%   $163.9119   $163.91   $163.90   $163.90  
  7 purchase totals = $713.58       $763.1710   $763.17   $763.20   $763.00