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 $192.26   3.606%   $199.1929   $199.19   $199.20   $199.20  
  Purchase #2 $53.51   11.805%   $59.8269   $59.83   $59.85   $59.80  
  Purchase #3 $196.89   8.646%   $213.9131   $213.91   $213.90   $213.90  
  Purchase #4 $49.97   8.148%   $54.0416   $54.04   $54.05   $54.00  
  Purchase #5 $107.96   6.619%   $115.1059   $115.11   $115.10   $115.10  
  Purchase #6 $239.77   7.202%   $257.0382   $257.04   $257.05   $257.00  
  Purchase #7 $165.27   7.182%   $177.1397   $177.14   $177.15   $177.10  
  7 purchase totals = $1,005.63       $1,076.2583   $1,076.26   $1,076.30   $1,076.10