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	$100.93	10.435%	$111.462	$111.46	$111.45	$111.50
Purchase #2	$106.52	7.753%	$114.7785	$114.78	$114.80	$114.80
Purchase #3	$31.54	7.385%	$33.8692	$33.87	$33.85	$33.90
Purchase #4	$96.46	11.476%	$107.5297	$107.53	$107.55	$107.50
Purchase #5	$94.80	10.864%	$105.0991	$105.10	$105.10	$105.10
Purchase #6	$220.73	8.756%	$240.0571	$240.06	$240.05	$240.10
Purchase #7	$147.56	12.658%	$166.2381	$166.24	$166.25	$166.20
7 purchase totals =	$798.54		$879.0337	$879.04	$879.05	$879.10