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	$240.73	6.512%	$256.4063	$256.41	$256.40	$256.40
Purchase #2	$201.52	9.742%	$221.1521	$221.15	$221.15	$221.20
Purchase #3	$115.86	13.216%	$131.1721	$131.17	$131.15	$131.20
Purchase #4	$193.37	4.268%	$201.623	$201.62	$201.60	$201.60
Purchase #5	$58.54	3.318%	$60.4824	$60.48	$60.50	$60.50
Purchase #6	$75.41	8.111%	$81.5265	$81.53	$81.55	$81.50
Purchase #7	$57.48	11.562%	$64.1258	$64.13	$64.15	$64.10
7 purchase totals =	$942.91		$1,016.4882	$1,016.49	$1,016.50	$1,016.50