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	$153.83	10.838%	$170.5021	$170.50	$170.50	$170.50
Purchase #2	$69.34	13.865%	$78.954	$78.95	$78.95	$79.00
Purchase #3	$46.76	11.644%	$52.2047	$52.20	$52.20	$52.20
Purchase #4	$25.69	12.566%	$28.9182	$28.92	$28.90	$28.90
Purchase #5	$180.85	5.695%	$191.1494	$191.15	$191.15	$191.10
Purchase #6	$69.57	5.477%	$73.3803	$73.38	$73.40	$73.40
Purchase #7	$71.35	12.774%	$80.4642	$80.46	$80.45	$80.50
7 purchase totals =	$617.39		$675.5729	$675.56	$675.55	$675.60