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	$72.37	8.842%	$78.769	$78.77	$78.75	$78.80
Purchase #2	$213.73	4.126%	$222.5485	$222.55	$222.55	$222.50
Purchase #3	$75.61	9.681%	$82.9298	$82.93	$82.95	$82.90
Purchase #4	$139.40	4.144%	$145.1767	$145.18	$145.20	$145.20
Purchase #5	$192.65	5.241%	$202.7468	$202.75	$202.75	$202.70
Purchase #6	$13.92	10.469%	$15.3773	$15.38	$15.40	$15.40
Purchase #7	$72.71	10.802%	$80.5641	$80.56	$80.55	$80.60
7 purchase totals =	$780.39		$828.1122	$828.12	$828.15	$828.10