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	$72.67	7.368%	$78.0243	$78.02	$78.00	$78.00
Purchase #2	$35.61	12.209%	$39.9576	$39.96	$39.95	$40.00
Purchase #3	$199.28	10.483%	$220.1705	$220.17	$220.15	$220.20
Purchase #4	$165.29	10.227%	$182.1942	$182.19	$182.20	$182.20
Purchase #5	$226.88	6.213%	$240.9761	$240.98	$241.00	$241.00
Purchase #6	$146.91	3.837%	$152.5469	$152.55	$152.55	$152.50
Purchase #7	$80.63	12.777%	$90.9321	$90.93	$90.95	$90.90
7 purchase totals =	$927.27		$1,004.8017	$1,004.80	$1,004.80	$1,004.80