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 $178.94   13.773%   $203.5854   $203.59   $203.60   $203.60  
  Purchase #2 $234.37   12.694%   $264.1209   $264.12   $264.10   $264.10  
  Purchase #3 $224.69   8.849%   $244.5728   $244.57   $244.55   $244.60  
  Purchase #4 $129.67   3.524%   $134.2396   $134.24   $134.25   $134.20  
  Purchase #5 $167.77   6.586%   $178.8193   $178.82   $178.80   $178.80  
  Purchase #6 $250.99   13.141%   $283.9726   $283.97   $283.95   $284.00  
  Purchase #7 $241.87   9.664%   $265.2443   $265.24   $265.25   $265.20  
  7 purchase totals = $1,428.30       $1,574.5549   $1,574.55   $1,574.50   $1,574.50