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	$37.82	12.306%	$42.4741	$42.47	$42.45	$42.50
Purchase #2	$17.98	4.830%	$18.8484	$18.85	$18.85	$18.80
Purchase #3	$48.61	7.215%	$52.1172	$52.12	$52.10	$52.10
Purchase #4	$232.66	3.829%	$241.5686	$241.57	$241.55	$241.60
Purchase #5	$83.95	9.711%	$92.1024	$92.10	$92.10	$92.10
Purchase #6	$226.30	8.567%	$245.6871	$245.69	$245.70	$245.70
Purchase #7	$40.84	4.391%	$42.6333	$42.63	$42.65	$42.60
7 purchase totals =	$688.16		$735.4311	$735.43	$735.40	$735.40