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	$92.46	7.215%	$99.131	$99.13	$99.15	$99.10
Purchase #2	$100.61	6.267%	$106.9152	$106.92	$106.90	$106.90
Purchase #3	$94.79	10.318%	$104.5704	$104.57	$104.55	$104.60
Purchase #4	$125.74	6.540%	$133.9634	$133.96	$133.95	$134.00
Purchase #5	$104.81	10.133%	$115.4304	$115.43	$115.45	$115.40
Purchase #6	$179.61	3.465%	$185.8335	$185.83	$185.85	$185.80
Purchase #7	$89.81	5.870%	$95.0818	$95.08	$95.10	$95.10
7 purchase totals =	$787.83		$840.9257	$840.92	$840.95	$840.90