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	$99.37	4.155%	$103.4988	$103.50	$103.50	$103.50
Purchase #2	$142.92	9.714%	$156.8032	$156.80	$156.80	$156.80
Purchase #3	$102.49	8.774%	$111.4825	$111.48	$111.50	$111.50
Purchase #4	$76.88	13.465%	$87.2319	$87.23	$87.25	$87.20
Purchase #5	$93.64	7.621%	$100.7763	$100.78	$100.80	$100.80
Purchase #6	$243.86	8.322%	$264.154	$264.15	$264.15	$264.20
Purchase #7	$66.70	10.831%	$73.9243	$73.92	$73.90	$73.90
7 purchase totals =	$825.86		$897.8710	$897.86	$897.90	$897.90