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	$43.53	4.484%	$45.4819	$45.48	$45.50	$45.50
Purchase #2	$91.45	6.515%	$97.408	$97.41	$97.40	$97.40
Purchase #3	$98.33	13.482%	$111.5869	$111.59	$111.60	$111.60
Purchase #4	$177.64	10.874%	$196.9566	$196.96	$196.95	$197.00
Purchase #5	$245.77	13.472%	$278.8801	$278.88	$278.90	$278.90
Purchase #6	$91.79	11.348%	$102.2063	$102.21	$102.20	$102.20
Purchase #7	$50.88	12.699%	$57.3413	$57.34	$57.35	$57.30
7 purchase totals =	$799.39		$889.8611	$889.87	$889.90	$889.90