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	$105.81	8.790%	$115.1107	$115.11	$115.10	$115.10
Purchase #2	$233.26	7.768%	$251.3796	$251.38	$251.40	$251.40
Purchase #3	$90.33	10.311%	$99.6439	$99.64	$99.65	$99.60
Purchase #4	$209.70	12.672%	$236.2732	$236.27	$236.25	$236.30
Purchase #5	$50.44	7.404%	$54.1746	$54.17	$54.15	$54.20
Purchase #6	$98.35	11.139%	$109.3052	$109.31	$109.30	$109.30
Purchase #7	$196.54	4.497%	$205.3784	$205.38	$205.40	$205.40
7 purchase totals =	$984.43		$1,071.2656	$1,071.26	$1,071.25	$1,071.30