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	$75.46	11.732%	$84.313	$84.31	$84.30	$84.30
Purchase #2	$178.34	10.342%	$196.7839	$196.78	$196.80	$196.80
Purchase #3	$91.90	7.632%	$98.9138	$98.91	$98.90	$98.90
Purchase #4	$151.68	5.167%	$159.5173	$159.52	$159.50	$159.50
Purchase #5	$212.56	4.437%	$221.9913	$221.99	$222.00	$222.00
Purchase #6	$33.79	10.816%	$37.4447	$37.44	$37.45	$37.40
Purchase #7	$98.43	6.151%	$104.4844	$104.48	$104.50	$104.50
7 purchase totals =	$842.16		$903.4484	$903.43	$903.45	$903.40