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	$36.55	9.191%	$39.9093	$39.91	$39.90	$39.90
Purchase #2	$141.36	4.479%	$147.6915	$147.69	$147.70	$147.70
Purchase #3	$135.33	5.300%	$142.5025	$142.50	$142.50	$142.50
Purchase #4	$165.79	13.361%	$187.9412	$187.94	$187.95	$187.90
Purchase #5	$154.32	8.780%	$167.8693	$167.87	$167.85	$167.90
Purchase #6	$176.96	6.469%	$188.4075	$188.41	$188.40	$188.40
Purchase #7	$163.34	3.826%	$169.5894	$169.59	$169.60	$169.60
7 purchase totals =	$973.65		$1,043.9107	$1,043.91	$1,043.90	$1,043.90