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	$84.69	11.158%	$94.1397	$94.14	$94.15	$94.10
Purchase #2	$31.58	8.287%	$34.197	$34.20	$34.20	$34.20
Purchase #3	$204.62	10.380%	$225.8596	$225.86	$225.85	$225.90
Purchase #4	$38.90	11.630%	$43.4241	$43.42	$43.40	$43.40
Purchase #5	$60.40	12.293%	$67.825	$67.83	$67.85	$67.80
Purchase #6	$110.46	9.219%	$120.6433	$120.64	$120.65	$120.60
Purchase #7	$90.62	9.362%	$99.1038	$99.10	$99.10	$99.10
7 purchase totals =	$621.27		$685.1925	$685.19	$685.20	$685.10