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	$244.62	11.720%	$273.2895	$273.29	$273.30	$273.30
Purchase #2	$151.78	5.839%	$160.6424	$160.64	$160.65	$160.60
Purchase #3	$204.39	9.215%	$223.2245	$223.22	$223.20	$223.20
Purchase #4	$229.56	4.805%	$240.5904	$240.59	$240.60	$240.60
Purchase #5	$150.90	13.411%	$171.1372	$171.14	$171.15	$171.10
Purchase #6	$182.34	13.201%	$206.4107	$206.41	$206.40	$206.40
Purchase #7	$77.57	11.108%	$86.1865	$86.19	$86.20	$86.20
7 purchase totals =	$1,241.16		$1,361.4812	$1,361.48	$1,361.50	$1,361.40