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	$51.31	6.264%	$54.5241	$54.52	$54.50	$54.50
Purchase #2	$93.34	8.227%	$101.0191	$101.02	$101.00	$101.00
Purchase #3	$181.74	12.183%	$203.8814	$203.88	$203.90	$203.90
Purchase #4	$29.48	9.818%	$32.3743	$32.37	$32.35	$32.40
Purchase #5	$70.73	8.283%	$76.5886	$76.59	$76.60	$76.60
Purchase #6	$142.42	6.697%	$151.9579	$151.96	$151.95	$152.00
Purchase #7	$85.73	4.715%	$89.7722	$89.77	$89.75	$89.80
7 purchase totals =	$654.75		$710.1176	$710.11	$710.05	$710.20