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	$154.36	6.435%	$164.2931	$164.29	$164.30	$164.30
Purchase #2	$96.99	9.707%	$106.4048	$106.40	$106.40	$106.40
Purchase #3	$134.76	8.454%	$146.1526	$146.15	$146.15	$146.20
Purchase #4	$199.50	11.754%	$222.9492	$222.95	$222.95	$222.90
Purchase #5	$98.46	12.713%	$110.9772	$110.98	$111.00	$111.00
Purchase #6	$75.81	12.592%	$85.356	$85.36	$85.35	$85.40
Purchase #7	$241.55	13.307%	$273.6931	$273.69	$273.70	$273.70
7 purchase totals =	$1,001.43		$1,109.8260	$1,109.82	$1,109.85	$1,109.90