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	$250.93	8.774%	$272.9466	$272.95	$272.95	$272.90
Purchase #2	$93.77	5.356%	$98.7923	$98.79	$98.80	$98.80
Purchase #3	$101.56	3.574%	$105.1898	$105.19	$105.20	$105.20
Purchase #4	$58.51	8.519%	$63.4945	$63.49	$63.50	$63.50
Purchase #5	$123.55	12.780%	$139.3397	$139.34	$139.35	$139.30
Purchase #6	$121.48	4.591%	$127.0571	$127.06	$127.05	$127.10
Purchase #7	$68.39	4.562%	$71.51	$71.51	$71.50	$71.50
7 purchase totals =	$818.19		$878.3300	$878.33	$878.35	$878.30