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	$33.81	5.168%	$35.5573	$35.56	$35.55	$35.60
Purchase #2	$245.48	11.817%	$274.4884	$274.49	$274.50	$274.50
Purchase #3	$44.62	13.183%	$50.5023	$50.50	$50.50	$50.50
Purchase #4	$210.34	9.426%	$230.1666	$230.17	$230.15	$230.20
Purchase #5	$79.89	13.184%	$90.4227	$90.42	$90.40	$90.40
Purchase #6	$78.78	5.124%	$82.8167	$82.82	$82.80	$82.80
Purchase #7	$41.98	9.678%	$46.0428	$46.04	$46.05	$46.00
7 purchase totals =	$734.90		$809.9968	$810.00	$809.95	$810.00