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	$94.73	7.361%	$101.7031	$101.70	$101.70	$101.70
Purchase #2	$131.48	12.218%	$147.5442	$147.54	$147.55	$147.50
Purchase #3	$123.72	12.379%	$139.0353	$139.04	$139.05	$139.00
Purchase #4	$228.50	12.305%	$256.6169	$256.62	$256.60	$256.60
Purchase #5	$64.87	9.604%	$71.1001	$71.10	$71.10	$71.10
Purchase #6	$74.71	10.423%	$82.497	$82.50	$82.50	$82.50
Purchase #7	$78.55	3.790%	$81.527	$81.53	$81.55	$81.50
7 purchase totals =	$796.56		$880.0236	$880.03	$880.05	$879.90