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	$83.45	6.696%	$89.0378	$89.04	$89.05	$89.00
Purchase #2	$206.69	13.243%	$234.062	$234.06	$234.05	$234.10
Purchase #3	$173.98	4.623%	$182.0231	$182.02	$182.00	$182.00
Purchase #4	$68.48	13.409%	$77.6625	$77.66	$77.65	$77.70
Purchase #5	$119.27	4.191%	$124.2686	$124.27	$124.25	$124.30
Purchase #6	$168.28	12.331%	$189.0306	$189.03	$189.05	$189.00
Purchase #7	$65.37	11.345%	$72.7862	$72.79	$72.80	$72.80
7 purchase totals =	$885.52		$968.8708	$968.87	$968.85	$968.90