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	$50.60	12.108%	$56.7266	$56.73	$56.75	$56.70
Purchase #2	$168.63	10.270%	$185.9483	$185.95	$185.95	$185.90
Purchase #3	$190.54	3.185%	$196.6087	$196.61	$196.60	$196.60
Purchase #4	$25.34	10.777%	$28.0709	$28.07	$28.05	$28.10
Purchase #5	$120.84	5.570%	$127.5708	$127.57	$127.55	$127.60
Purchase #6	$78.41	10.790%	$86.8704	$86.87	$86.85	$86.90
Purchase #7	$115.32	13.301%	$130.6587	$130.66	$130.65	$130.70
7 purchase totals =	$749.68		$812.4544	$812.46	$812.40	$812.50