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	$40.85	4.837%	$42.8259	$42.83	$42.85	$42.80
Purchase #2	$123.79	12.596%	$139.3826	$139.38	$139.40	$139.40
Purchase #3	$110.41	8.614%	$119.9207	$119.92	$119.90	$119.90
Purchase #4	$150.32	5.812%	$159.0566	$159.06	$159.05	$159.10
Purchase #5	$237.76	11.485%	$265.0667	$265.07	$265.05	$265.10
Purchase #6	$57.61	11.721%	$64.3625	$64.36	$64.35	$64.40
Purchase #7	$43.80	5.170%	$46.0645	$46.06	$46.05	$46.10
7 purchase totals =	$764.54		$836.6795	$836.68	$836.65	$836.80