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	$119.33	10.215%	$131.5196	$131.52	$131.50	$131.50
Purchase #2	$173.71	13.179%	$196.6032	$196.60	$196.60	$196.60
Purchase #3	$168.37	9.805%	$184.8787	$184.88	$184.90	$184.90
Purchase #4	$46.55	5.767%	$49.2345	$49.23	$49.25	$49.20
Purchase #5	$37.35	8.596%	$40.5606	$40.56	$40.55	$40.60
Purchase #6	$71.46	7.827%	$77.0532	$77.05	$77.05	$77.10
Purchase #7	$191.35	6.270%	$203.3476	$203.35	$203.35	$203.30
7 purchase totals =	$808.12		$883.1974	$883.19	$883.20	$883.20