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	$139.99	10.279%	$154.3796	$154.38	$154.40	$154.40
Purchase #2	$33.73	6.404%	$35.8901	$35.89	$35.90	$35.90
Purchase #3	$208.79	13.370%	$236.7052	$236.71	$236.70	$236.70
Purchase #4	$112.32	9.566%	$123.0645	$123.06	$123.05	$123.10
Purchase #5	$208.51	10.281%	$229.9469	$229.95	$229.95	$229.90
Purchase #6	$168.39	12.572%	$189.56	$189.56	$189.55	$189.60
Purchase #7	$91.94	11.532%	$102.5425	$102.54	$102.55	$102.50
7 purchase totals =	$963.67		$1,072.0888	$1,072.09	$1,072.10	$1,072.10