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 $118.82   5.688%   $125.5785   $125.58   $125.60   $125.60  
  Purchase #2 $243.99   10.794%   $270.3263   $270.33   $270.35   $270.30  
  Purchase #3 $84.33   6.741%   $90.0147   $90.01   $90.00   $90.00  
  Purchase #4 $8.36   11.407%   $9.3136   $9.31   $9.30   $9.30  
  Purchase #5 $112.99   11.858%   $126.3884   $126.39   $126.40   $126.40  
  Purchase #6 $41.62   5.675%   $43.9819   $43.98   $44.00   $44.00  
  Purchase #7 $167.41   5.383%   $176.4217   $176.42   $176.40   $176.40  
  7 purchase totals = $777.52       $842.0251   $842.02   $842.05   $842.00