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	$198.52	7.480%	$213.3693	$213.37	$213.35	$213.40
Purchase #2	$71.81	12.712%	$80.9385	$80.94	$80.95	$80.90
Purchase #3	$65.78	8.104%	$71.1108	$71.11	$71.10	$71.10
Purchase #4	$153.87	13.371%	$174.444	$174.44	$174.45	$174.40
Purchase #5	$128.31	10.468%	$141.7415	$141.74	$141.75	$141.70
Purchase #6	$73.30	12.803%	$82.6846	$82.68	$82.70	$82.70
Purchase #7	$71.27	10.235%	$78.5645	$78.56	$78.55	$78.60
7 purchase totals =	$762.86		$842.8532	$842.84	$842.85	$842.80