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	$53.83	3.365%	$55.6414	$55.64	$55.65	$55.60
Purchase #2	$104.25	10.665%	$115.3683	$115.37	$115.35	$115.40
Purchase #3	$155.89	12.421%	$175.2531	$175.25	$175.25	$175.30
Purchase #4	$78.28	6.672%	$83.5028	$83.50	$83.50	$83.50
Purchase #5	$246.55	4.765%	$258.2981	$258.30	$258.30	$258.30
Purchase #6	$64.70	10.318%	$71.3757	$71.38	$71.40	$71.40
Purchase #7	$57.46	12.616%	$64.7092	$64.71	$64.70	$64.70
7 purchase totals =	$760.96		$824.1486	$824.15	$824.15	$824.20