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	$32.80	5.341%	$34.5518	$34.55	$34.55	$34.60
Purchase #2	$25.56	10.780%	$28.3154	$28.32	$28.30	$28.30
Purchase #3	$232.45	4.571%	$243.0753	$243.08	$243.10	$243.10
Purchase #4	$82.75	9.197%	$90.3605	$90.36	$90.35	$90.40
Purchase #5	$67.98	8.413%	$73.6992	$73.70	$73.70	$73.70
Purchase #6	$90.32	10.306%	$99.6284	$99.63	$99.65	$99.60
Purchase #7	$53.78	9.561%	$58.9219	$58.92	$58.90	$58.90
7 purchase totals =	$585.64		$628.5525	$628.56	$628.55	$628.60