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	$27.35	12.599%	$30.7958	$30.80	$30.80	$30.80
Purchase #2	$64.57	12.656%	$72.742	$72.74	$72.75	$72.70
Purchase #3	$84.78	5.207%	$89.1945	$89.19	$89.20	$89.20
Purchase #4	$51.54	11.693%	$57.5666	$57.57	$57.55	$57.60
Purchase #5	$42.94	11.398%	$47.8343	$47.83	$47.85	$47.80
Purchase #6	$246.73	11.284%	$274.571	$274.57	$274.55	$274.60
Purchase #7	$250.40	10.385%	$276.404	$276.40	$276.40	$276.40
7 purchase totals =	$768.31		$849.1082	$849.10	$849.10	$849.10