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	$79.70	6.751%	$85.0805	$85.08	$85.10	$85.10
Purchase #2	$56.72	7.645%	$61.0562	$61.06	$61.05	$61.10
Purchase #3	$121.40	10.362%	$133.9795	$133.98	$134.00	$134.00
Purchase #4	$148.38	7.725%	$159.8424	$159.84	$159.85	$159.80
Purchase #5	$59.54	10.654%	$65.8834	$65.88	$65.90	$65.90
Purchase #6	$79.40	12.213%	$89.0971	$89.10	$89.10	$89.10
Purchase #7	$84.82	8.679%	$92.1815	$92.18	$92.20	$92.20
7 purchase totals =	$629.96		$687.1206	$687.12	$687.20	$687.20