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	$6.66	11.557%	$7.4297	$7.43	$7.45	$7.40
Purchase #2	$113.72	8.185%	$123.028	$123.03	$123.05	$123.00
Purchase #3	$131.96	6.300%	$140.2735	$140.27	$140.25	$140.30
Purchase #4	$82.60	7.130%	$88.4894	$88.49	$88.50	$88.50
Purchase #5	$105.95	3.538%	$109.6985	$109.70	$109.70	$109.70
Purchase #6	$224.44	4.179%	$233.8193	$233.82	$233.80	$233.80
Purchase #7	$187.32	3.648%	$194.1534	$194.15	$194.15	$194.20
7 purchase totals =	$852.65		$896.8918	$896.89	$896.90	$896.90