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	$20.86	4.267%	$21.7501	$21.75	$21.75	$21.80
Purchase #2	$222.61	12.278%	$249.9421	$249.94	$249.95	$249.90
Purchase #3	$155.67	3.348%	$160.8818	$160.88	$160.90	$160.90
Purchase #4	$20.53	3.790%	$21.3081	$21.31	$21.30	$21.30
Purchase #5	$209.74	10.752%	$232.2912	$232.29	$232.30	$232.30
Purchase #6	$157.67	7.369%	$169.2887	$169.29	$169.30	$169.30
Purchase #7	$158.56	3.500%	$164.1096	$164.11	$164.10	$164.10
7 purchase totals =	$945.64		$1,019.5716	$1,019.57	$1,019.60	$1,019.60