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	$209.30	13.815%	$238.2148	$238.21	$238.20	$238.20
Purchase #2	$82.55	7.435%	$88.6876	$88.69	$88.70	$88.70
Purchase #3	$26.50	13.781%	$30.152	$30.15	$30.15	$30.20
Purchase #4	$218.58	10.832%	$242.2566	$242.26	$242.25	$242.30
Purchase #5	$182.85	3.494%	$189.2388	$189.24	$189.25	$189.20
Purchase #6	$217.29	12.818%	$245.1422	$245.14	$245.15	$245.10
Purchase #7	$83.73	7.419%	$89.9419	$89.94	$89.95	$89.90
7 purchase totals =	$1,020.80		$1,123.6339	$1,123.63	$1,123.65	$1,123.60