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	$123.33	8.772%	$134.1485	$134.15	$134.15	$134.10
Purchase #2	$130.56	7.374%	$140.1875	$140.19	$140.20	$140.20
Purchase #3	$169.47	12.334%	$190.3724	$190.37	$190.35	$190.40
Purchase #4	$237.29	12.431%	$266.7875	$266.79	$266.80	$266.80
Purchase #5	$239.98	10.336%	$264.7843	$264.78	$264.80	$264.80
Purchase #6	$156.66	5.842%	$165.8121	$165.81	$165.80	$165.80
Purchase #7	$131.27	5.481%	$138.4649	$138.46	$138.45	$138.50
7 purchase totals =	$1,188.56		$1,300.5572	$1,300.55	$1,300.55	$1,300.60