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	$89.46	3.483%	$92.5759	$92.58	$92.60	$92.60
Purchase #2	$115.89	13.323%	$131.33	$131.33	$131.35	$131.30
Purchase #3	$156.88	5.356%	$165.2825	$165.28	$165.30	$165.30
Purchase #4	$21.52	3.759%	$22.3289	$22.33	$22.35	$22.30
Purchase #5	$222.90	9.429%	$243.9172	$243.92	$243.90	$243.90
Purchase #6	$68.82	12.778%	$77.6138	$77.61	$77.60	$77.60
Purchase #7	$77.52	10.573%	$85.7162	$85.72	$85.70	$85.70
7 purchase totals =	$752.99		$818.7645	$818.77	$818.80	$818.70