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	$48.38	6.672%	$51.6079	$51.61	$51.60	$51.60
Purchase #2	$37.94	9.380%	$41.4988	$41.50	$41.50	$41.50
Purchase #3	$54.39	7.852%	$58.6607	$58.66	$58.65	$58.70
Purchase #4	$147.64	7.309%	$158.431	$158.43	$158.45	$158.40
Purchase #5	$188.71	5.398%	$198.8966	$198.90	$198.90	$198.90
Purchase #6	$57.44	7.638%	$61.8273	$61.83	$61.85	$61.80
Purchase #7	$171.29	9.132%	$186.9322	$186.93	$186.95	$186.90
7 purchase totals =	$705.79		$757.8545	$757.86	$757.90	$757.80