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 $97.68   9.475%   $106.9352   $106.94   $106.95   $106.90  
  Purchase #2 $141.31   10.633%   $156.3355   $156.34   $156.35   $156.30  
  Purchase #3 $105.71   13.139%   $119.5992   $119.60   $119.60   $119.60  
  Purchase #4 $238.49   11.747%   $266.5054   $266.51   $266.50   $266.50  
  Purchase #5 $131.44   12.150%   $147.41   $147.41   $147.40   $147.40  
  Purchase #6 $67.76   4.472%   $70.7902   $70.79   $70.80   $70.80  
  Purchase #7 $149.69   12.259%   $168.0405   $168.04   $168.05   $168.00  
  7 purchase totals = $932.08       $1,035.6160   $1,035.63   $1,035.65   $1,035.50