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	$131.96	3.131%	$136.0917	$136.09	$136.10	$136.10
Purchase #2	$80.98	12.564%	$91.1543	$91.15	$91.15	$91.20
Purchase #3	$45.78	6.737%	$48.8642	$48.86	$48.85	$48.90
Purchase #4	$167.77	8.428%	$181.9097	$181.91	$181.90	$181.90
Purchase #5	$146.89	7.253%	$157.5439	$157.54	$157.55	$157.50
Purchase #6	$42.66	7.282%	$45.7665	$45.77	$45.75	$45.80
Purchase #7	$25.67	8.402%	$27.8268	$27.83	$27.85	$27.80
7 purchase totals =	$641.71		$689.1571	$689.15	$689.15	$689.20