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	$51.77	12.145%	$58.0575	$58.06	$58.05	$58.10
Purchase #2	$144.38	4.806%	$151.3189	$151.32	$151.30	$151.30
Purchase #3	$219.94	13.650%	$249.9618	$249.96	$249.95	$250.00
Purchase #4	$231.30	7.361%	$248.326	$248.33	$248.35	$248.30
Purchase #5	$127.53	6.752%	$136.1408	$136.14	$136.15	$136.10
Purchase #6	$99.62	9.669%	$109.2523	$109.25	$109.25	$109.30
Purchase #7	$148.76	7.227%	$159.5109	$159.51	$159.50	$159.50
7 purchase totals =	$1,023.30		$1,112.5682	$1,112.57	$1,112.55	$1,112.60