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	$67.27	9.762%	$73.8369	$73.84	$73.85	$73.80
Purchase #2	$164.90	8.454%	$178.8406	$178.84	$178.85	$178.80
Purchase #3	$193.97	5.505%	$204.648	$204.65	$204.65	$204.60
Purchase #4	$89.30	11.752%	$99.7945	$99.79	$99.80	$99.80
Purchase #5	$141.90	7.216%	$152.1395	$152.14	$152.15	$152.10
Purchase #6	$90.30	11.353%	$100.5518	$100.55	$100.55	$100.60
Purchase #7	$86.83	9.611%	$95.1752	$95.18	$95.20	$95.20
7 purchase totals =	$834.47		$904.9865	$904.99	$905.05	$904.90