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	$243.33	12.448%	$273.6197	$273.62	$273.60	$273.60
Purchase #2	$62.62	5.228%	$65.8938	$65.89	$65.90	$65.90
Purchase #3	$242.56	3.286%	$250.5305	$250.53	$250.55	$250.50
Purchase #4	$187.53	6.151%	$199.065	$199.07	$199.05	$199.10
Purchase #5	$5.48	8.776%	$5.9609	$5.96	$5.95	$6.00
Purchase #6	$63.90	11.709%	$71.3821	$71.38	$71.40	$71.40
Purchase #7	$182.84	4.367%	$190.8246	$190.82	$190.80	$190.80
7 purchase totals =	$988.26		$1,057.2766	$1,057.27	$1,057.25	$1,057.30