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 $204.75   13.616%   $232.6288   $232.63   $232.65   $232.60  
  Purchase #2 $188.73   4.122%   $196.5095   $196.51   $196.50   $196.50  
  Purchase #3 $222.94   13.430%   $252.8808   $252.88   $252.90   $252.90  
  Purchase #4 $66.96   3.152%   $69.0706   $69.07   $69.05   $69.10  
  Purchase #5 $118.45   7.368%   $127.1774   $127.18   $127.20   $127.20  
  Purchase #6 $90.53   7.414%   $97.2419   $97.24   $97.25   $97.20  
  Purchase #7 $30.55   8.257%   $33.0725   $33.07   $33.05   $33.10  
  7 purchase totals = $922.91       $1,008.5815   $1,008.58   $1,008.60   $1,008.60