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	$34.35	9.851%	$37.7338	$37.73	$37.75	$37.70
Purchase #2	$216.43	4.479%	$226.1239	$226.12	$226.10	$226.10
Purchase #3	$171.44	4.138%	$178.5342	$178.53	$178.55	$178.50
Purchase #4	$40.34	12.566%	$45.4091	$45.41	$45.40	$45.40
Purchase #5	$146.43	5.678%	$154.7443	$154.74	$154.75	$154.70
Purchase #6	$205.75	11.498%	$229.4071	$229.41	$229.40	$229.40
Purchase #7	$149.31	12.225%	$167.5631	$167.56	$167.55	$167.60
7 purchase totals =	$964.05		$1,039.5155	$1,039.50	$1,039.50	$1,039.40