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	$40.25	5.116%	$42.3092	$42.31	$42.30	$42.30
Purchase #2	$82.39	7.493%	$88.5635	$88.56	$88.55	$88.60
Purchase #3	$171.74	13.237%	$194.4732	$194.47	$194.45	$194.50
Purchase #4	$46.83	11.196%	$52.0731	$52.07	$52.05	$52.10
Purchase #5	$81.65	6.353%	$86.8372	$86.84	$86.85	$86.80
Purchase #6	$165.90	12.639%	$186.8681	$186.87	$186.85	$186.90
Purchase #7	$48.66	11.871%	$54.4364	$54.44	$54.45	$54.40
7 purchase totals =	$637.42		$705.5607	$705.56	$705.50	$705.60