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	$5.59	4.459%	$5.8393	$5.84	$5.85	$5.80
Purchase #2	$160.99	3.259%	$166.2367	$166.24	$166.25	$166.20
Purchase #3	$172.99	9.474%	$189.3791	$189.38	$189.40	$189.40
Purchase #4	$152.72	11.159%	$169.762	$169.76	$169.75	$169.80
Purchase #5	$246.67	4.548%	$257.8886	$257.89	$257.90	$257.90
Purchase #6	$115.32	10.850%	$127.8322	$127.83	$127.85	$127.80
Purchase #7	$86.80	4.578%	$90.7737	$90.77	$90.75	$90.80
7 purchase totals =	$941.08		$1,007.7116	$1,007.71	$1,007.75	$1,007.70