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	$229.98	3.374%	$237.7395	$237.74	$237.75	$237.70
Purchase #2	$129.40	13.228%	$146.517	$146.52	$146.50	$146.50
Purchase #3	$33.90	5.398%	$35.7299	$35.73	$35.75	$35.70
Purchase #4	$33.94	5.821%	$35.9156	$35.92	$35.90	$35.90
Purchase #5	$20.85	4.613%	$21.8118	$21.81	$21.80	$21.80
Purchase #6	$73.46	13.244%	$83.189	$83.19	$83.20	$83.20
Purchase #7	$53.69	11.534%	$59.8826	$59.88	$59.90	$59.90
7 purchase totals =	$575.22		$620.7854	$620.79	$620.80	$620.70