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	$89.37	12.381%	$100.4349	$100.43	$100.45	$100.40
Purchase #2	$154.55	8.407%	$167.543	$167.54	$167.55	$167.50
Purchase #3	$146.50	6.872%	$156.5675	$156.57	$156.55	$156.60
Purchase #4	$107.51	9.560%	$117.788	$117.79	$117.80	$117.80
Purchase #5	$22.74	10.591%	$25.1484	$25.15	$25.15	$25.10
Purchase #6	$240.44	9.713%	$263.7939	$263.79	$263.80	$263.80
Purchase #7	$91.42	9.115%	$99.7529	$99.75	$99.75	$99.80
7 purchase totals =	$852.53		$931.0286	$931.02	$931.05	$931.00