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	$36.53	13.847%	$41.5883	$41.59	$41.60	$41.60
Purchase #2	$226.61	6.225%	$240.7165	$240.72	$240.70	$240.70
Purchase #3	$31.46	4.335%	$32.8238	$32.82	$32.80	$32.80
Purchase #4	$33.33	5.697%	$35.2288	$35.23	$35.25	$35.20
Purchase #5	$28.40	12.291%	$31.8906	$31.89	$31.90	$31.90
Purchase #6	$85.44	4.489%	$89.2754	$89.28	$89.30	$89.30
Purchase #7	$247.66	8.775%	$269.3922	$269.39	$269.40	$269.40
7 purchase totals =	$689.43		$740.9156	$740.92	$740.95	$740.90