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	$89.97	13.833%	$102.4156	$102.42	$102.40	$102.40
Purchase #2	$106.99	4.819%	$112.1458	$112.15	$112.15	$112.10
Purchase #3	$98.67	6.839%	$105.418	$105.42	$105.40	$105.40
Purchase #4	$102.50	6.694%	$109.3614	$109.36	$109.35	$109.40
Purchase #5	$246.36	4.801%	$258.1877	$258.19	$258.20	$258.20
Purchase #6	$81.29	9.657%	$89.1402	$89.14	$89.15	$89.10
Purchase #7	$110.86	9.419%	$121.3019	$121.30	$121.30	$121.30
7 purchase totals =	$836.64		$897.9706	$897.98	$897.95	$897.90