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	$20.27	6.415%	$21.5703	$21.57	$21.55	$21.60
Purchase #2	$20.82	10.165%	$22.9364	$22.94	$22.95	$22.90
Purchase #3	$75.61	9.641%	$82.8996	$82.90	$82.90	$82.90
Purchase #4	$46.69	3.686%	$48.411	$48.41	$48.40	$48.40
Purchase #5	$248.74	3.148%	$256.5703	$256.57	$256.55	$256.60
Purchase #6	$106.90	4.157%	$111.3438	$111.34	$111.35	$111.30
Purchase #7	$178.59	6.354%	$189.9376	$189.94	$189.95	$189.90
7 purchase totals =	$697.62		$733.6690	$733.67	$733.65	$733.60