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	$119.94	6.836%	$128.1391	$128.14	$128.15	$128.10
Purchase #2	$191.61	3.802%	$198.895	$198.90	$198.90	$198.90
Purchase #3	$206.79	4.745%	$216.6022	$216.60	$216.60	$216.60
Purchase #4	$231.59	4.761%	$242.616	$242.62	$242.60	$242.60
Purchase #5	$73.32	7.292%	$78.6665	$78.67	$78.65	$78.70
Purchase #6	$137.73	12.768%	$155.3154	$155.32	$155.30	$155.30
Purchase #7	$45.34	11.621%	$50.609	$50.61	$50.60	$50.60
7 purchase totals =	$1,006.32		$1,070.8432	$1,070.86	$1,070.80	$1,070.80