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	$209.83	5.682%	$221.7525	$221.75	$221.75	$221.80
Purchase #2	$42.33	5.234%	$44.5456	$44.55	$44.55	$44.50
Purchase #3	$120.85	9.158%	$131.9174	$131.92	$131.90	$131.90
Purchase #4	$164.73	7.301%	$176.7569	$176.76	$176.75	$176.80
Purchase #5	$39.50	9.445%	$43.2308	$43.23	$43.25	$43.20
Purchase #6	$164.35	12.227%	$184.4451	$184.45	$184.45	$184.40
Purchase #7	$109.27	3.604%	$113.2081	$113.21	$113.20	$113.20
7 purchase totals =	$850.86		$915.8564	$915.87	$915.85	$915.80