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	$183.31	5.462%	$193.3224	$193.32	$193.30	$193.30
Purchase #2	$56.60	7.228%	$60.691	$60.69	$60.70	$60.70
Purchase #3	$39.31	7.647%	$42.316	$42.32	$42.30	$42.30
Purchase #4	$179.34	9.498%	$196.3737	$196.37	$196.35	$196.40
Purchase #5	$76.65	4.204%	$79.8724	$79.87	$79.85	$79.90
Purchase #6	$103.59	13.872%	$117.96	$117.96	$117.95	$118.00
Purchase #7	$143.46	3.793%	$148.9014	$148.90	$148.90	$148.90
7 purchase totals =	$782.26		$839.4369	$839.43	$839.35	$839.50