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	$20.37	13.457%	$23.1112	$23.11	$23.10	$23.10
Purchase #2	$10.37	10.673%	$11.4768	$11.48	$11.50	$11.50
Purchase #3	$105.59	3.296%	$109.0702	$109.07	$109.05	$109.10
Purchase #4	$6.61	13.250%	$7.4858	$7.49	$7.50	$7.50
Purchase #5	$91.75	12.592%	$103.3032	$103.30	$103.30	$103.30
Purchase #6	$92.90	3.520%	$96.1701	$96.17	$96.15	$96.20
Purchase #7	$79.56	5.533%	$83.9621	$83.96	$83.95	$84.00
7 purchase totals =	$407.15		$434.5794	$434.58	$434.55	$434.70