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	$244.88	11.652%	$273.4134	$273.41	$273.40	$273.40
Purchase #2	$40.89	4.261%	$42.6323	$42.63	$42.65	$42.60
Purchase #3	$197.66	7.529%	$212.5418	$212.54	$212.55	$212.50
Purchase #4	$113.34	5.586%	$119.6712	$119.67	$119.65	$119.70
Purchase #5	$145.41	3.748%	$150.86	$150.86	$150.85	$150.90
Purchase #6	$218.73	10.476%	$241.6442	$241.64	$241.65	$241.60
Purchase #7	$101.91	12.388%	$114.5346	$114.53	$114.55	$114.50
7 purchase totals =	$1,062.82		$1,155.2975	$1,155.28	$1,155.30	$1,155.20