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	$120.67	6.692%	$128.7452	$128.75	$128.75	$128.70
Purchase #2	$96.80	10.661%	$107.1198	$107.12	$107.10	$107.10
Purchase #3	$27.29	10.843%	$30.2491	$30.25	$30.25	$30.20
Purchase #4	$138.46	3.851%	$143.7921	$143.79	$143.80	$143.80
Purchase #5	$42.53	6.340%	$45.2264	$45.23	$45.25	$45.20
Purchase #6	$130.47	5.685%	$137.8872	$137.89	$137.90	$137.90
Purchase #7	$118.33	7.360%	$127.0391	$127.04	$127.05	$127.00
7 purchase totals =	$674.55		$720.0589	$720.07	$720.10	$719.90