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 $183.78   11.329%   $204.6004   $204.60   $204.60   $204.60  
  Purchase #2 $164.67   3.629%   $170.6459   $170.65   $170.65   $170.60  
  Purchase #3 $147.30   11.586%   $164.3662   $164.37   $164.35   $164.40  
  Purchase #4 $62.77   12.553%   $70.6495   $70.65   $70.65   $70.60  
  Purchase #5 $63.87   11.858%   $71.4437   $71.44   $71.45   $71.40  
  Purchase #6 $137.88   3.606%   $142.852   $142.85   $142.85   $142.90  
  Purchase #7 $241.99   3.867%   $251.3478   $251.35   $251.35   $251.30  
  7 purchase totals = $1,002.26       $1,075.9055   $1,075.91   $1,075.90   $1,075.80