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	$128.44	13.333%	$145.5649	$145.56	$145.55	$145.60
Purchase #2	$200.72	9.578%	$219.945	$219.95	$219.95	$219.90
Purchase #3	$82.47	10.427%	$91.0691	$91.07	$91.05	$91.10
Purchase #4	$80.74	3.488%	$83.5562	$83.56	$83.55	$83.60
Purchase #5	$115.86	11.831%	$129.5674	$129.57	$129.55	$129.60
Purchase #6	$102.95	7.804%	$110.9842	$110.98	$111.00	$111.00
Purchase #7	$213.70	5.162%	$224.7312	$224.73	$224.75	$224.70
7 purchase totals =	$924.88		$1,005.4180	$1,005.42	$1,005.40	$1,005.50