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	$25.28	7.200%	$27.1002	$27.10	$27.10	$27.10
Purchase #2	$246.84	12.109%	$276.7299	$276.73	$276.75	$276.70
Purchase #3	$93.50	12.751%	$105.4222	$105.42	$105.40	$105.40
Purchase #4	$153.50	12.475%	$172.6491	$172.65	$172.65	$172.60
Purchase #5	$105.53	6.432%	$112.3177	$112.32	$112.30	$112.30
Purchase #6	$51.73	13.820%	$58.8791	$58.88	$58.90	$58.90
Purchase #7	$100.43	4.742%	$105.1924	$105.19	$105.20	$105.20
7 purchase totals =	$776.81		$858.2906	$858.29	$858.30	$858.20