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	$75.70	3.282%	$78.1845	$78.18	$78.20	$78.20
Purchase #2	$88.91	13.697%	$101.088	$101.09	$101.10	$101.10
Purchase #3	$118.84	5.446%	$125.312	$125.31	$125.30	$125.30
Purchase #4	$145.42	11.333%	$161.9004	$161.90	$161.90	$161.90
Purchase #5	$206.72	7.768%	$222.778	$222.78	$222.80	$222.80
Purchase #6	$135.47	8.131%	$146.4851	$146.49	$146.50	$146.50
Purchase #7	$85.95	11.826%	$96.1144	$96.11	$96.10	$96.10
7 purchase totals =	$857.01		$931.8624	$931.86	$931.90	$931.90