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	$62.29	3.776%	$64.6421	$64.64	$64.65	$64.60
Purchase #2	$103.67	8.384%	$112.3617	$112.36	$112.35	$112.40
Purchase #3	$151.88	12.741%	$171.231	$171.23	$171.25	$171.20
Purchase #4	$53.43	11.785%	$59.7267	$59.73	$59.75	$59.70
Purchase #5	$31.46	6.791%	$33.5964	$33.60	$33.60	$33.60
Purchase #6	$201.68	6.502%	$214.7932	$214.79	$214.80	$214.80
Purchase #7	$117.56	13.287%	$133.1802	$133.18	$133.20	$133.20
7 purchase totals =	$721.97		$789.5313	$789.53	$789.60	$789.50