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	$131.84	13.868%	$150.1236	$150.12	$150.10	$150.10
Purchase #2	$54.84	9.190%	$59.8798	$59.88	$59.90	$59.90
Purchase #3	$188.28	9.225%	$205.6488	$205.65	$205.65	$205.60
Purchase #4	$38.91	9.653%	$42.666	$42.67	$42.65	$42.70
Purchase #5	$159.83	4.352%	$166.7858	$166.79	$166.80	$166.80
Purchase #6	$62.43	9.560%	$68.3983	$68.40	$68.40	$68.40
Purchase #7	$126.73	5.513%	$133.7166	$133.72	$133.70	$133.70
7 purchase totals =	$762.86		$827.2189	$827.23	$827.20	$827.20