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	$168.76	5.474%	$177.9979	$178.00	$178.00	$178.00
Purchase #2	$55.97	10.457%	$61.8228	$61.82	$61.80	$61.80
Purchase #3	$26.49	6.635%	$28.2476	$28.25	$28.25	$28.20
Purchase #4	$78.25	10.495%	$86.4623	$86.46	$86.45	$86.50
Purchase #5	$55.41	7.793%	$59.7281	$59.73	$59.75	$59.70
Purchase #6	$189.31	5.700%	$200.1007	$200.10	$200.10	$200.10
Purchase #7	$248.47	12.526%	$279.5934	$279.59	$279.60	$279.60
7 purchase totals =	$822.66		$893.9528	$893.95	$893.95	$893.90