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	$142.44	3.380%	$147.2545	$147.25	$147.25	$147.30
Purchase #2	$19.37	7.304%	$20.7848	$20.78	$20.80	$20.80
Purchase #3	$31.54	6.528%	$33.5989	$33.60	$33.60	$33.60
Purchase #4	$147.73	7.326%	$158.5527	$158.55	$158.55	$158.60
Purchase #5	$216.96	5.704%	$229.3354	$229.34	$229.35	$229.30
Purchase #6	$104.46	7.113%	$111.8902	$111.89	$111.90	$111.90
Purchase #7	$9.70	3.767%	$10.0654	$10.07	$10.05	$10.10
7 purchase totals =	$672.20		$711.4819	$711.48	$711.50	$711.60