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	$75.54	12.755%	$85.1751	$85.18	$85.20	$85.20
Purchase #2	$202.32	11.788%	$226.1695	$226.17	$226.15	$226.20
Purchase #3	$222.73	11.333%	$247.972	$247.97	$247.95	$248.00
Purchase #4	$209.42	6.136%	$222.27	$222.27	$222.25	$222.30
Purchase #5	$161.91	4.573%	$169.3141	$169.31	$169.30	$169.30
Purchase #6	$152.98	12.177%	$171.6084	$171.61	$171.60	$171.60
Purchase #7	$156.61	8.444%	$169.8341	$169.83	$169.85	$169.80
7 purchase totals =	$1,181.51		$1,292.3432	$1,292.34	$1,292.30	$1,292.40