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	$140.29	13.415%	$159.1099	$159.11	$159.10	$159.10
Purchase #2	$65.28	5.372%	$68.7868	$68.79	$68.80	$68.80
Purchase #3	$82.56	8.369%	$89.4694	$89.47	$89.45	$89.50
Purchase #4	$97.48	3.393%	$100.7875	$100.79	$100.80	$100.80
Purchase #5	$86.76	3.448%	$89.7515	$89.75	$89.75	$89.80
Purchase #6	$6.74	11.829%	$7.5373	$7.54	$7.55	$7.50
Purchase #7	$133.35	10.309%	$147.0971	$147.10	$147.10	$147.10
7 purchase totals =	$612.46		$662.5395	$662.55	$662.55	$662.60