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	$109.55	12.417%	$123.1528	$123.15	$123.15	$123.20
Purchase #2	$182.48	4.630%	$190.9288	$190.93	$190.95	$190.90
Purchase #3	$70.31	11.108%	$78.12	$78.12	$78.10	$78.10
Purchase #4	$32.75	8.337%	$35.4804	$35.48	$35.50	$35.50
Purchase #5	$188.33	4.435%	$196.6824	$196.68	$196.70	$196.70
Purchase #6	$206.31	12.254%	$231.5912	$231.59	$231.60	$231.60
Purchase #7	$247.61	12.631%	$278.8856	$278.89	$278.90	$278.90
7 purchase totals =	$1,037.34		$1,134.8412	$1,134.84	$1,134.90	$1,134.90