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	$135.65	4.595%	$141.8831	$141.88	$141.90	$141.90
Purchase #2	$182.85	11.781%	$204.3916	$204.39	$204.40	$204.40
Purchase #3	$114.49	11.287%	$127.4125	$127.41	$127.40	$127.40
Purchase #4	$81.40	4.609%	$85.1517	$85.15	$85.15	$85.20
Purchase #5	$91.40	7.617%	$98.3619	$98.36	$98.35	$98.40
Purchase #6	$163.33	9.826%	$179.3788	$179.38	$179.40	$179.40
Purchase #7	$172.36	7.389%	$185.0957	$185.10	$185.10	$185.10
7 purchase totals =	$941.48		$1,021.6753	$1,021.67	$1,021.70	$1,021.80