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	$227.37	11.299%	$253.0605	$253.06	$253.05	$253.10
Purchase #2	$172.74	6.159%	$183.3791	$183.38	$183.40	$183.40
Purchase #3	$136.92	12.489%	$154.0199	$154.02	$154.00	$154.00
Purchase #4	$246.27	13.180%	$278.7284	$278.73	$278.75	$278.70
Purchase #5	$100.50	6.700%	$107.2335	$107.23	$107.25	$107.20
Purchase #6	$73.25	6.817%	$78.2435	$78.24	$78.25	$78.20
Purchase #7	$147.56	13.727%	$167.8156	$167.82	$167.80	$167.80
7 purchase totals =	$1,104.61		$1,222.4805	$1,222.48	$1,222.50	$1,222.40