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	$43.69	4.262%	$45.5521	$45.55	$45.55	$45.60
Purchase #2	$189.48	12.296%	$212.7785	$212.78	$212.80	$212.80
Purchase #3	$38.36	7.293%	$41.1576	$41.16	$41.15	$41.20
Purchase #4	$235.44	5.676%	$248.8036	$248.80	$248.80	$248.80
Purchase #5	$125.98	12.812%	$142.1206	$142.12	$142.10	$142.10
Purchase #6	$58.98	13.683%	$67.0502	$67.05	$67.05	$67.10
Purchase #7	$68.93	11.852%	$77.0996	$77.10	$77.10	$77.10
7 purchase totals =	$760.86		$834.5622	$834.56	$834.55	$834.70