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	$19.69	6.454%	$20.9608	$20.96	$20.95	$21.00
Purchase #2	$105.86	10.825%	$117.3193	$117.32	$117.30	$117.30
Purchase #3	$62.70	8.334%	$67.9254	$67.93	$67.95	$67.90
Purchase #4	$200.56	5.206%	$211.0012	$211.00	$211.00	$211.00
Purchase #5	$41.93	9.427%	$45.8827	$45.88	$45.90	$45.90
Purchase #6	$156.94	5.563%	$165.6706	$165.67	$165.65	$165.70
Purchase #7	$158.92	5.165%	$167.1282	$167.13	$167.15	$167.10
7 purchase totals =	$746.60		$795.8882	$795.89	$795.90	$795.90