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	$180.90	5.601%	$191.0322	$191.03	$191.05	$191.00
Purchase #2	$58.72	12.611%	$66.1252	$66.13	$66.15	$66.10
Purchase #3	$99.61	9.724%	$109.2961	$109.30	$109.30	$109.30
Purchase #4	$140.46	8.393%	$152.2488	$152.25	$152.25	$152.20
Purchase #5	$33.35	13.403%	$37.8199	$37.82	$37.80	$37.80
Purchase #6	$201.71	13.449%	$228.838	$228.84	$228.85	$228.80
Purchase #7	$174.90	7.716%	$188.3953	$188.40	$188.40	$188.40
7 purchase totals =	$889.65		$973.7555	$973.77	$973.80	$973.60