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	$42.48	6.699%	$45.3257	$45.33	$45.35	$45.30
Purchase #2	$197.69	7.700%	$212.9121	$212.91	$212.90	$212.90
Purchase #3	$155.99	5.661%	$164.8206	$164.82	$164.80	$164.80
Purchase #4	$60.53	9.636%	$66.3627	$66.36	$66.35	$66.40
Purchase #5	$39.55	8.324%	$42.8421	$42.84	$42.85	$42.80
Purchase #6	$95.37	4.814%	$99.9611	$99.96	$99.95	$100.00
Purchase #7	$57.37	6.509%	$61.1042	$61.10	$61.10	$61.10
7 purchase totals =	$648.98		$693.3285	$693.32	$693.30	$693.30