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	$71.39	10.317%	$78.7553	$78.76	$78.75	$78.80
Purchase #2	$54.78	4.504%	$57.2473	$57.25	$57.25	$57.20
Purchase #3	$55.77	5.172%	$58.6544	$58.65	$58.65	$58.70
Purchase #4	$174.77	3.774%	$181.3658	$181.37	$181.35	$181.40
Purchase #5	$29.77	4.701%	$31.1695	$31.17	$31.15	$31.20
Purchase #6	$52.74	12.223%	$59.1864	$59.19	$59.20	$59.20
Purchase #7	$210.98	8.206%	$228.293	$228.29	$228.30	$228.30
7 purchase totals =	$650.20		$694.6717	$694.68	$694.65	$694.80