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	$35.31	8.809%	$38.4205	$38.42	$38.40	$38.40
Purchase #2	$179.56	11.842%	$200.8235	$200.82	$200.80	$200.80
Purchase #3	$81.91	11.278%	$91.1478	$91.15	$91.15	$91.10
Purchase #4	$184.41	8.715%	$200.4813	$200.48	$200.50	$200.50
Purchase #5	$170.84	10.429%	$188.6569	$188.66	$188.65	$188.70
Purchase #6	$57.99	9.459%	$63.4753	$63.48	$63.50	$63.50
Purchase #7	$79.86	3.566%	$82.7078	$82.71	$82.70	$82.70
7 purchase totals =	$789.88		$865.7131	$865.72	$865.70	$865.70