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	$121.61	11.605%	$135.7228	$135.72	$135.70	$135.70
Purchase #2	$102.56	11.526%	$114.3811	$114.38	$114.40	$114.40
Purchase #3	$147.95	5.763%	$156.4764	$156.48	$156.50	$156.50
Purchase #4	$27.74	12.364%	$31.1698	$31.17	$31.15	$31.20
Purchase #5	$69.49	4.583%	$72.6747	$72.67	$72.65	$72.70
Purchase #6	$83.59	10.166%	$92.0878	$92.09	$92.10	$92.10
Purchase #7	$169.76	12.109%	$190.3162	$190.32	$190.30	$190.30
7 purchase totals =	$722.70		$792.8288	$792.83	$792.80	$792.90