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	$77.36	10.310%	$85.3358	$85.34	$85.35	$85.30
Purchase #2	$104.89	6.715%	$111.9334	$111.93	$111.95	$111.90
Purchase #3	$37.55	11.468%	$41.8562	$41.86	$41.85	$41.90
Purchase #4	$35.98	11.301%	$40.0461	$40.05	$40.05	$40.00
Purchase #5	$218.58	3.710%	$226.6893	$226.69	$226.70	$226.70
Purchase #6	$243.57	3.676%	$252.5236	$252.52	$252.50	$252.50
Purchase #7	$96.99	3.851%	$100.7251	$100.73	$100.75	$100.70
7 purchase totals =	$814.92		$859.1095	$859.12	$859.15	$859.00