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	$165.37	13.173%	$187.1542	$187.15	$187.15	$187.20
Purchase #2	$134.91	5.671%	$142.5607	$142.56	$142.55	$142.60
Purchase #3	$136.64	3.841%	$141.8883	$141.89	$141.90	$141.90
Purchase #4	$245.62	10.262%	$270.8255	$270.83	$270.85	$270.80
Purchase #5	$50.90	10.506%	$56.2476	$56.25	$56.25	$56.20
Purchase #6	$85.26	5.188%	$89.6833	$89.68	$89.70	$89.70
Purchase #7	$240.68	13.868%	$274.0575	$274.06	$274.05	$274.10
7 purchase totals =	$1,059.38		$1,162.4171	$1,162.42	$1,162.45	$1,162.50