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	$74.87	4.787%	$78.454	$78.45	$78.45	$78.50
Purchase #2	$210.44	12.802%	$237.3805	$237.38	$237.40	$237.40
Purchase #3	$90.65	4.261%	$94.5126	$94.51	$94.50	$94.50
Purchase #4	$96.32	8.782%	$104.7788	$104.78	$104.80	$104.80
Purchase #5	$194.93	6.143%	$206.9045	$206.90	$206.90	$206.90
Purchase #6	$129.33	7.810%	$139.4307	$139.43	$139.45	$139.40
Purchase #7	$104.71	5.435%	$110.401	$110.40	$110.40	$110.40
7 purchase totals =	$901.25		$971.8621	$971.85	$971.90	$971.90