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	$91.70	9.239%	$100.1722	$100.17	$100.15	$100.20
Purchase #2	$182.61	9.503%	$199.9634	$199.96	$199.95	$200.00
Purchase #3	$102.35	10.454%	$113.0497	$113.05	$113.05	$113.00
Purchase #4	$55.62	10.216%	$61.3021	$61.30	$61.30	$61.30
Purchase #5	$215.27	3.166%	$222.0854	$222.09	$222.10	$222.10
Purchase #6	$191.34	3.703%	$198.4253	$198.43	$198.45	$198.40
Purchase #7	$246.26	12.702%	$277.5399	$277.54	$277.55	$277.50
7 purchase totals =	$1,085.15		$1,172.5380	$1,172.54	$1,172.55	$1,172.50