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	$146.91	6.538%	$156.515	$156.52	$156.50	$156.50
Purchase #2	$202.56	9.616%	$222.0382	$222.04	$222.05	$222.00
Purchase #3	$79.73	12.841%	$89.9681	$89.97	$89.95	$90.00
Purchase #4	$80.50	4.170%	$83.8569	$83.86	$83.85	$83.90
Purchase #5	$55.76	4.567%	$58.3066	$58.31	$58.30	$58.30
Purchase #6	$6.67	4.642%	$6.9796	$6.98	$7.00	$7.00
Purchase #7	$192.94	3.736%	$200.1482	$200.15	$200.15	$200.10
7 purchase totals =	$765.07		$817.8126	$817.83	$817.80	$817.80