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	$112.81	6.265%	$119.8775	$119.88	$119.90	$119.90
Purchase #2	$187.72	6.281%	$199.5107	$199.51	$199.50	$199.50
Purchase #3	$64.60	11.793%	$72.2183	$72.22	$72.20	$72.20
Purchase #4	$67.70	4.192%	$70.538	$70.54	$70.55	$70.50
Purchase #5	$18.98	12.301%	$21.3147	$21.31	$21.30	$21.30
Purchase #6	$229.52	4.148%	$239.0405	$239.04	$239.05	$239.00
Purchase #7	$89.30	13.252%	$101.134	$101.13	$101.15	$101.10
7 purchase totals =	$770.63		$823.6337	$823.63	$823.65	$823.50