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	$34.90	6.374%	$37.1245	$37.12	$37.10	$37.10
Purchase #2	$82.81	4.443%	$86.4892	$86.49	$86.50	$86.50
Purchase #3	$168.67	9.869%	$185.316	$185.32	$185.30	$185.30
Purchase #4	$58.66	8.112%	$63.4185	$63.42	$63.40	$63.40
Purchase #5	$212.65	12.828%	$239.9287	$239.93	$239.95	$239.90
Purchase #6	$80.39	10.601%	$88.9121	$88.91	$88.90	$88.90
Purchase #7	$151.56	11.370%	$168.7924	$168.79	$168.80	$168.80
7 purchase totals =	$789.64		$869.9814	$869.98	$869.95	$869.90