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	$30.38	3.267%	$31.3725	$31.37	$31.35	$31.40
Purchase #2	$160.86	13.450%	$182.4957	$182.50	$182.50	$182.50
Purchase #3	$69.56	12.573%	$78.3058	$78.31	$78.30	$78.30
Purchase #4	$162.90	12.849%	$183.831	$183.83	$183.85	$183.80
Purchase #5	$192.92	8.680%	$209.6655	$209.67	$209.65	$209.70
Purchase #6	$120.78	7.801%	$130.202	$130.20	$130.20	$130.20
Purchase #7	$247.50	10.458%	$273.3836	$273.38	$273.40	$273.40
7 purchase totals =	$984.90		$1,089.2561	$1,089.26	$1,089.25	$1,089.30