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	$150.46	13.722%	$171.1061	$171.11	$171.10	$171.10
Purchase #2	$110.56	12.285%	$124.1423	$124.14	$124.15	$124.10
Purchase #3	$7.31	11.478%	$8.149	$8.15	$8.15	$8.10
Purchase #4	$140.34	7.327%	$150.6227	$150.62	$150.60	$150.60
Purchase #5	$128.89	6.658%	$137.4715	$137.47	$137.45	$137.50
Purchase #6	$64.37	4.117%	$67.0201	$67.02	$67.00	$67.00
Purchase #7	$134.77	13.280%	$152.6675	$152.67	$152.65	$152.70
7 purchase totals =	$736.70		$811.1792	$811.18	$811.10	$811.10