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	$103.86	5.102%	$109.1589	$109.16	$109.15	$109.20
Purchase #2	$198.74	3.820%	$206.3319	$206.33	$206.35	$206.30
Purchase #3	$137.64	4.546%	$143.8971	$143.90	$143.90	$143.90
Purchase #4	$188.31	10.487%	$208.0581	$208.06	$208.05	$208.10
Purchase #5	$43.77	4.118%	$45.5724	$45.57	$45.55	$45.60
Purchase #6	$115.96	11.529%	$129.329	$129.33	$129.35	$129.30
Purchase #7	$142.49	12.869%	$160.827	$160.83	$160.85	$160.80
7 purchase totals =	$930.77		$1,003.1744	$1,003.18	$1,003.20	$1,003.20