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	$111.37	10.764%	$123.3579	$123.36	$123.35	$123.40
Purchase #2	$100.71	10.439%	$111.2231	$111.22	$111.20	$111.20
Purchase #3	$204.34	9.162%	$223.0616	$223.06	$223.05	$223.10
Purchase #4	$131.49	3.833%	$136.53	$136.53	$136.55	$136.50
Purchase #5	$196.92	3.129%	$203.0816	$203.08	$203.10	$203.10
Purchase #6	$137.73	9.383%	$150.6532	$150.65	$150.65	$150.70
Purchase #7	$182.88	4.444%	$191.0072	$191.01	$191.00	$191.00
7 purchase totals =	$1,065.44		$1,138.9146	$1,138.91	$1,138.90	$1,139.00