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	$175.85	3.165%	$181.4157	$181.42	$181.40	$181.40
Purchase #2	$97.44	8.140%	$105.3716	$105.37	$105.35	$105.40
Purchase #3	$238.41	6.518%	$253.9496	$253.95	$253.95	$253.90
Purchase #4	$68.50	6.161%	$72.7203	$72.72	$72.70	$72.70
Purchase #5	$164.91	7.264%	$176.8891	$176.89	$176.90	$176.90
Purchase #6	$57.74	7.804%	$62.246	$62.25	$62.25	$62.20
Purchase #7	$90.66	3.732%	$94.0434	$94.04	$94.05	$94.00
7 purchase totals =	$893.51		$946.6357	$946.64	$946.60	$946.50