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	$70.64	11.104%	$78.4839	$78.48	$78.50	$78.50
Purchase #2	$198.96	10.530%	$219.9105	$219.91	$219.90	$219.90
Purchase #3	$108.67	4.108%	$113.1342	$113.13	$113.15	$113.10
Purchase #4	$219.44	12.741%	$247.3989	$247.40	$247.40	$247.40
Purchase #5	$175.93	12.725%	$198.3171	$198.32	$198.30	$198.30
Purchase #6	$35.78	8.148%	$38.6954	$38.70	$38.70	$38.70
Purchase #7	$239.53	4.754%	$250.9173	$250.92	$250.90	$250.90
7 purchase totals =	$1,048.95		$1,146.8573	$1,146.86	$1,146.85	$1,146.80