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	$73.92	13.393%	$83.8201	$83.82	$83.80	$83.80
Purchase #2	$239.69	10.261%	$264.2846	$264.28	$264.30	$264.30
Purchase #3	$194.79	7.268%	$208.9473	$208.95	$208.95	$208.90
Purchase #4	$243.39	10.666%	$269.35	$269.35	$269.35	$269.40
Purchase #5	$207.76	9.761%	$228.0395	$228.04	$228.05	$228.00
Purchase #6	$33.74	10.456%	$37.2679	$37.27	$37.25	$37.30
Purchase #7	$84.48	5.841%	$89.4145	$89.41	$89.40	$89.40
7 purchase totals =	$1,077.77		$1,181.1239	$1,181.12	$1,181.10	$1,181.10