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	$42.40	7.810%	$45.7114	$45.71	$45.70	$45.70
Purchase #2	$80.28	11.319%	$89.3669	$89.37	$89.35	$89.40
Purchase #3	$156.32	5.262%	$164.5456	$164.55	$164.55	$164.50
Purchase #4	$65.83	12.302%	$73.9284	$73.93	$73.95	$73.90
Purchase #5	$38.80	3.751%	$40.2554	$40.26	$40.25	$40.30
Purchase #6	$89.84	5.245%	$94.5521	$94.55	$94.55	$94.60
Purchase #7	$85.69	12.596%	$96.4835	$96.48	$96.50	$96.50
7 purchase totals =	$559.16		$604.8433	$604.85	$604.85	$604.90