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	$131.33	9.119%	$143.306	$143.31	$143.30	$143.30
Purchase #2	$191.51	10.496%	$211.6109	$211.61	$211.60	$211.60
Purchase #3	$140.58	11.370%	$156.5639	$156.56	$156.55	$156.60
Purchase #4	$37.69	3.805%	$39.1241	$39.12	$39.10	$39.10
Purchase #5	$64.39	10.649%	$71.2469	$71.25	$71.25	$71.20
Purchase #6	$99.63	8.363%	$107.9621	$107.96	$107.95	$108.00
Purchase #7	$213.38	13.610%	$242.421	$242.42	$242.40	$242.40
7 purchase totals =	$878.51		$972.2349	$972.23	$972.15	$972.20