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	$142.71	9.505%	$156.2746	$156.27	$156.25	$156.30
Purchase #2	$85.50	4.420%	$89.2791	$89.28	$89.30	$89.30
Purchase #3	$190.56	6.413%	$202.7806	$202.78	$202.80	$202.80
Purchase #4	$27.35	10.236%	$30.1495	$30.15	$30.15	$30.10
Purchase #5	$237.75	13.630%	$270.1553	$270.16	$270.15	$270.20
Purchase #6	$211.47	12.737%	$238.4049	$238.40	$238.40	$238.40
Purchase #7	$63.53	12.114%	$71.226	$71.23	$71.25	$71.20
7 purchase totals =	$958.87		$1,058.2700	$1,058.27	$1,058.30	$1,058.30