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	$101.60	7.419%	$109.1377	$109.14	$109.15	$109.10
Purchase #2	$106.98	4.420%	$111.7085	$111.71	$111.70	$111.70
Purchase #3	$75.88	12.412%	$85.2982	$85.30	$85.30	$85.30
Purchase #4	$59.72	10.172%	$65.7947	$65.79	$65.80	$65.80
Purchase #5	$203.55	12.345%	$228.6782	$228.68	$228.70	$228.70
Purchase #6	$202.33	6.279%	$215.0343	$215.03	$215.05	$215.00
Purchase #7	$55.86	12.289%	$62.7246	$62.72	$62.70	$62.70
7 purchase totals =	$805.92		$878.3762	$878.37	$878.40	$878.30