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	$83.37	12.743%	$93.9938	$93.99	$94.00	$94.00
Purchase #2	$42.78	3.618%	$44.3278	$44.33	$44.35	$44.30
Purchase #3	$142.53	9.159%	$155.5843	$155.58	$155.60	$155.60
Purchase #4	$174.43	12.441%	$196.1308	$196.13	$196.15	$196.10
Purchase #5	$80.57	12.822%	$90.9007	$90.90	$90.90	$90.90
Purchase #6	$59.57	9.757%	$65.3822	$65.38	$65.40	$65.40
Purchase #7	$182.71	12.502%	$205.5524	$205.55	$205.55	$205.60
7 purchase totals =	$765.96		$851.8720	$851.86	$851.95	$851.90