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	$26.27	11.230%	$29.2201	$29.22	$29.20	$29.20
Purchase #2	$128.48	12.200%	$144.1546	$144.15	$144.15	$144.20
Purchase #3	$231.73	5.567%	$244.6304	$244.63	$244.65	$244.60
Purchase #4	$169.47	7.414%	$182.0345	$182.03	$182.05	$182.00
Purchase #5	$76.77	7.804%	$82.7611	$82.76	$82.75	$82.80
Purchase #6	$196.56	6.537%	$209.4091	$209.41	$209.40	$209.40
Purchase #7	$89.81	11.476%	$100.1166	$100.12	$100.10	$100.10
7 purchase totals =	$919.09		$992.3264	$992.32	$992.30	$992.30