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	$100.61	7.866%	$108.524	$108.52	$108.50	$108.50
Purchase #2	$233.84	12.571%	$263.236	$263.24	$263.25	$263.20
Purchase #3	$138.98	11.541%	$155.0197	$155.02	$155.00	$155.00
Purchase #4	$170.33	4.850%	$178.591	$178.59	$178.60	$178.60
Purchase #5	$76.49	5.770%	$80.9035	$80.90	$80.90	$80.90
Purchase #6	$250.97	7.549%	$269.9157	$269.92	$269.90	$269.90
Purchase #7	$151.34	9.152%	$165.1906	$165.19	$165.20	$165.20
7 purchase totals =	$1,122.56		$1,221.3805	$1,221.38	$1,221.35	$1,221.30