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	$135.45	12.593%	$152.5072	$152.51	$152.50	$152.50
Purchase #2	$93.90	6.402%	$99.9115	$99.91	$99.90	$99.90
Purchase #3	$179.91	6.267%	$191.185	$191.19	$191.20	$191.20
Purchase #4	$162.57	12.814%	$183.4017	$183.40	$183.40	$183.40
Purchase #5	$62.49	4.116%	$65.0621	$65.06	$65.05	$65.10
Purchase #6	$25.96	11.707%	$28.9991	$29.00	$29.00	$29.00
Purchase #7	$94.27	9.367%	$103.1003	$103.10	$103.10	$103.10
7 purchase totals =	$754.55		$824.1669	$824.17	$824.15	$824.20