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 $97.88   8.576%   $106.2742   $106.27   $106.25   $106.30  
  Purchase #2 $215.63   9.460%   $236.0286   $236.03   $236.05   $236.00  
  Purchase #3 $123.98   8.539%   $134.5667   $134.57   $134.55   $134.60  
  Purchase #4 $153.96   13.642%   $174.9632   $174.96   $174.95   $175.00  
  Purchase #5 $39.91   5.656%   $42.1673   $42.17   $42.15   $42.20  
  Purchase #6 $192.37   11.120%   $213.7615   $213.76   $213.75   $213.80  
  Purchase #7 $170.62   10.495%   $188.5266   $188.53   $188.55   $188.50  
  7 purchase totals = $994.35       $1,096.2881   $1,096.29   $1,096.25   $1,096.40