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	$32.46	7.872%	$35.0153	$35.02	$35.00	$35.00
Purchase #2	$36.44	10.167%	$40.1449	$40.14	$40.15	$40.10
Purchase #3	$239.94	10.369%	$264.8194	$264.82	$264.80	$264.80
Purchase #4	$131.89	11.635%	$147.2354	$147.24	$147.25	$147.20
Purchase #5	$170.97	13.769%	$194.5109	$194.51	$194.50	$194.50
Purchase #6	$50.27	13.233%	$56.9222	$56.92	$56.90	$56.90
Purchase #7	$75.35	13.126%	$85.2404	$85.24	$85.25	$85.20
7 purchase totals =	$737.32		$823.8885	$823.89	$823.85	$823.70