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	$39.62	7.653%	$42.6521	$42.65	$42.65	$42.70
Purchase #2	$197.87	6.268%	$210.2725	$210.27	$210.25	$210.30
Purchase #3	$197.41	5.133%	$207.5431	$207.54	$207.55	$207.50
Purchase #4	$117.64	5.316%	$123.8937	$123.89	$123.90	$123.90
Purchase #5	$154.96	3.575%	$160.4998	$160.50	$160.50	$160.50
Purchase #6	$193.29	6.181%	$205.2373	$205.24	$205.25	$205.20
Purchase #7	$30.82	3.221%	$31.8127	$31.81	$31.80	$31.80
7 purchase totals =	$931.61		$981.9112	$981.90	$981.90	$981.90