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	$86.65	5.439%	$91.3629	$91.36	$91.35	$91.40
Purchase #2	$79.75	13.155%	$90.2411	$90.24	$90.25	$90.20
Purchase #3	$237.49	3.534%	$245.8829	$245.88	$245.90	$245.90
Purchase #4	$113.94	12.264%	$127.9136	$127.91	$127.90	$127.90
Purchase #5	$79.97	7.525%	$85.9877	$85.99	$86.00	$86.00
Purchase #6	$62.99	4.155%	$65.6072	$65.61	$65.60	$65.60
Purchase #7	$146.80	3.494%	$151.9292	$151.93	$151.95	$151.90
7 purchase totals =	$807.59		$858.9246	$858.92	$858.95	$858.90