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	$93.56	6.816%	$99.937	$99.94	$99.95	$99.90
Purchase #2	$37.31	13.571%	$42.3733	$42.37	$42.35	$42.40
Purchase #3	$102.59	10.733%	$113.601	$113.60	$113.60	$113.60
Purchase #4	$199.38	6.760%	$212.8581	$212.86	$212.85	$212.90
Purchase #5	$37.59	8.352%	$40.7295	$40.73	$40.75	$40.70
Purchase #6	$217.35	10.287%	$239.7088	$239.71	$239.70	$239.70
Purchase #7	$61.30	12.406%	$68.9049	$68.90	$68.90	$68.90
7 purchase totals =	$749.08		$818.1126	$818.11	$818.10	$818.10