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	$18.73	6.799%	$20.0035	$20.00	$20.00	$20.00
Purchase #2	$11.47	11.206%	$12.7553	$12.76	$12.75	$12.80
Purchase #3	$43.93	3.759%	$45.5813	$45.58	$45.60	$45.60
Purchase #4	$79.72	8.336%	$86.3655	$86.37	$86.35	$86.40
Purchase #5	$156.68	3.624%	$162.3581	$162.36	$162.35	$162.40
Purchase #6	$212.89	7.515%	$228.8887	$228.89	$228.90	$228.90
Purchase #7	$105.74	4.570%	$110.5723	$110.57	$110.55	$110.60
7 purchase totals =	$629.16		$666.5247	$666.53	$666.50	$666.70