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	$28.94	7.490%	$31.1076	$31.11	$31.10	$31.10
Purchase #2	$211.82	7.510%	$227.7277	$227.73	$227.75	$227.70
Purchase #3	$125.57	11.172%	$139.5987	$139.60	$139.60	$139.60
Purchase #4	$35.30	12.166%	$39.5946	$39.59	$39.60	$39.60
Purchase #5	$167.33	10.849%	$185.4836	$185.48	$185.50	$185.50
Purchase #6	$66.82	7.147%	$71.5956	$71.60	$71.60	$71.60
Purchase #7	$8.58	9.137%	$9.364	$9.36	$9.35	$9.40
7 purchase totals =	$644.36		$704.4718	$704.47	$704.50	$704.50