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	$105.81	3.860%	$109.8943	$109.89	$109.90	$109.90
Purchase #2	$88.52	12.465%	$99.554	$99.55	$99.55	$99.60
Purchase #3	$178.95	3.567%	$185.3331	$185.33	$185.35	$185.30
Purchase #4	$12.48	6.577%	$13.3008	$13.30	$13.30	$13.30
Purchase #5	$129.29	6.531%	$137.7339	$137.73	$137.75	$137.70
Purchase #6	$55.59	13.611%	$63.1564	$63.16	$63.15	$63.20
Purchase #7	$57.68	4.634%	$60.3529	$60.35	$60.35	$60.40
7 purchase totals =	$628.32		$669.3254	$669.31	$669.35	$669.40