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	$77.69	6.547%	$82.7764	$82.78	$82.80	$82.80
Purchase #2	$139.44	6.394%	$148.3558	$148.36	$148.35	$148.40
Purchase #3	$169.84	12.524%	$191.1108	$191.11	$191.10	$191.10
Purchase #4	$185.50	7.728%	$199.8354	$199.84	$199.85	$199.80
Purchase #5	$128.53	10.836%	$142.4575	$142.46	$142.45	$142.50
Purchase #6	$85.44	12.329%	$95.9739	$95.97	$95.95	$96.00
Purchase #7	$50.60	11.141%	$56.2373	$56.24	$56.25	$56.20
7 purchase totals =	$837.04		$916.7471	$916.76	$916.75	$916.80