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	$10.84	13.437%	$12.2966	$12.30	$12.30	$12.30
Purchase #2	$190.57	4.240%	$198.6502	$198.65	$198.65	$198.70
Purchase #3	$160.46	4.138%	$167.0998	$167.10	$167.10	$167.10
Purchase #4	$96.61	5.287%	$101.7178	$101.72	$101.70	$101.70
Purchase #5	$75.28	4.176%	$78.4237	$78.42	$78.40	$78.40
Purchase #6	$158.88	5.415%	$167.4834	$167.48	$167.50	$167.50
Purchase #7	$91.96	5.386%	$96.913	$96.91	$96.90	$96.90
7 purchase totals =	$784.60		$822.5845	$822.58	$822.55	$822.60