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	$236.46	13.799%	$269.0891	$269.09	$269.10	$269.10
Purchase #2	$225.98	11.201%	$251.292	$251.29	$251.30	$251.30
Purchase #3	$179.40	11.647%	$200.2947	$200.29	$200.30	$200.30
Purchase #4	$45.98	11.630%	$51.3275	$51.33	$51.35	$51.30
Purchase #5	$223.50	4.526%	$233.6156	$233.62	$233.60	$233.60
Purchase #6	$162.72	5.142%	$171.0871	$171.09	$171.10	$171.10
Purchase #7	$90.79	8.692%	$98.6815	$98.68	$98.70	$98.70
7 purchase totals =	$1,164.83		$1,275.3875	$1,275.39	$1,275.45	$1,275.40