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	$59.98	11.834%	$67.078	$67.08	$67.10	$67.10
Purchase #2	$218.57	10.819%	$242.2171	$242.22	$242.20	$242.20
Purchase #3	$178.91	10.547%	$197.7796	$197.78	$197.80	$197.80
Purchase #4	$115.46	6.726%	$123.2258	$123.23	$123.25	$123.20
Purchase #5	$104.89	11.804%	$117.2712	$117.27	$117.25	$117.30
Purchase #6	$243.41	3.470%	$251.8563	$251.86	$251.85	$251.90
Purchase #7	$203.35	9.594%	$222.8594	$222.86	$222.85	$222.90
7 purchase totals =	$1,124.57		$1,222.2874	$1,222.30	$1,222.30	$1,222.40