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	$50.25	7.232%	$53.8841	$53.88	$53.90	$53.90
Purchase #2	$41.38	7.325%	$44.4111	$44.41	$44.40	$44.40
Purchase #3	$52.68	3.679%	$54.6181	$54.62	$54.60	$54.60
Purchase #4	$65.45	9.552%	$71.7018	$71.70	$71.70	$71.70
Purchase #5	$133.27	10.545%	$147.3233	$147.32	$147.30	$147.30
Purchase #6	$64.47	11.231%	$71.7106	$71.71	$71.70	$71.70
Purchase #7	$240.54	13.695%	$273.482	$273.48	$273.50	$273.50
7 purchase totals =	$648.04		$717.1310	$717.12	$717.10	$717.10