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	$80.89	10.314%	$89.233	$89.23	$89.25	$89.20
Purchase #2	$143.55	12.583%	$161.6129	$161.61	$161.60	$161.60
Purchase #3	$53.56	10.777%	$59.3322	$59.33	$59.35	$59.30
Purchase #4	$238.33	11.595%	$265.9644	$265.96	$265.95	$266.00
Purchase #5	$29.33	10.227%	$32.3296	$32.33	$32.35	$32.30
Purchase #6	$44.57	7.134%	$47.7496	$47.75	$47.75	$47.70
Purchase #7	$103.56	10.712%	$114.6533	$114.65	$114.65	$114.70
7 purchase totals =	$693.79		$770.8750	$770.86	$770.90	$770.80