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	$140.73	6.428%	$149.7761	$149.78	$149.80	$149.80
Purchase #2	$161.72	3.645%	$167.6147	$167.61	$167.60	$167.60
Purchase #3	$26.88	11.356%	$29.9325	$29.93	$29.95	$29.90
Purchase #4	$126.66	5.245%	$133.3033	$133.30	$133.30	$133.30
Purchase #5	$68.76	6.398%	$73.1593	$73.16	$73.15	$73.20
Purchase #6	$174.89	9.452%	$191.4206	$191.42	$191.40	$191.40
Purchase #7	$83.73	7.865%	$90.3154	$90.32	$90.30	$90.30
7 purchase totals =	$783.37		$835.5219	$835.52	$835.50	$835.50