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	$159.59	6.646%	$170.1964	$170.20	$170.20	$170.20
Purchase #2	$63.38	12.667%	$71.4083	$71.41	$71.40	$71.40
Purchase #3	$249.90	9.531%	$273.718	$273.72	$273.70	$273.70
Purchase #4	$144.30	5.820%	$152.6983	$152.70	$152.70	$152.70
Purchase #5	$232.27	9.572%	$254.5029	$254.50	$254.50	$254.50
Purchase #6	$43.64	12.193%	$48.961	$48.96	$48.95	$49.00
Purchase #7	$54.51	12.843%	$61.5107	$61.51	$61.50	$61.50
7 purchase totals =	$947.59		$1,032.9956	$1,033.00	$1,032.95	$1,033.00