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	$130.28	6.791%	$139.1273	$139.13	$139.15	$139.10
Purchase #2	$190.52	10.171%	$209.8978	$209.90	$209.90	$209.90
Purchase #3	$126.89	10.453%	$140.1538	$140.15	$140.15	$140.20
Purchase #4	$131.30	13.298%	$148.7603	$148.76	$148.75	$148.80
Purchase #5	$18.70	9.148%	$20.4107	$20.41	$20.40	$20.40
Purchase #6	$177.51	4.605%	$185.6843	$185.68	$185.70	$185.70
Purchase #7	$231.89	7.140%	$248.4469	$248.45	$248.45	$248.40
7 purchase totals =	$1,007.09		$1,092.4811	$1,092.48	$1,092.50	$1,092.50