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	$48.82	4.123%	$50.8328	$50.83	$50.85	$50.80
Purchase #2	$39.60	12.513%	$44.5551	$44.56	$44.55	$44.60
Purchase #3	$240.84	13.361%	$273.0186	$273.02	$273.00	$273.00
Purchase #4	$41.26	3.137%	$42.5543	$42.55	$42.55	$42.60
Purchase #5	$235.89	10.611%	$260.9203	$260.92	$260.90	$260.90
Purchase #6	$250.77	4.382%	$261.7587	$261.76	$261.75	$261.80
Purchase #7	$139.90	7.279%	$150.0833	$150.08	$150.10	$150.10
7 purchase totals =	$997.08		$1,083.7231	$1,083.72	$1,083.70	$1,083.80